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< > APPEARANCE/ MORPHOLOGY: HEAD AND NECK with literature reports for the West European Hedgehog: Use sub-contents list below, or simply scroll down the page to view findings.

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HEAD AND NECK - Editorial Comment

Editorial Comment (Editorial Overview Text Replicated on Overall Species page - Erinaceus europaeus - West European Hedgehog)

GENERAL HEAD STRUCTURE:
Adult:
The hedgehog has short, broad rounded ears, mainly hidden by hair and a long narrow snout with a moist black rhinarium (tip of the nose). The small broad skull contains a relatively small brain.
Newborn: Hoglet neonates are born with their ears sealed closed.

DENTITION:
Adult:
The adult dentition includes a total of 36 teeth, dental formula I3/2, C 1/1, P 3/2, M 3/3. The deciduous dentition includes 24 teeth; these are shed by 3-4 months of age. Dental abnormalities are not uncommon in Britain and may be particularly common in the population in New Zealand.

EYES:
Adult:
The eyes are bright black and of moderate size. They are neither enlarged for acute nocturnal vision nor reduced in size. They are normally somewhat prominent.
Newborn:
Hoglet neonates are born with their eyes sealed closed.

(References are available in detailed literature reports below)

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General Head Structure

Adult SUMMARY: The hedgehog has short broad rounded ears, mainly hidden by hair and a long narrow snout with a moist black rhinarium. The small broad skull contains a relatively small brain.
  •  "Postero-dorsal processes of maxillae short, not extending behind lachrimal foramena." This is one of the distinguishing features of Erinaceus europaeus as distinct from Erinaceus concolor - East European hedgehog. (J82.18.w1)
  • The brain case of the hedgehog is small and the front of the skull is blunt. (B52, B285.w1)
  • The skull is broad with well-developed zygomatic arches (cheek bones). (B228.1.w1)
  • Ears are short, broad and rounded, mainly hidden by hair. (B52, B258.w2, B255.2.w2, D30)
    • Ears are 2-3 cm (0.75-1.0 inches) long. (B254.2.w2)
    • As their names suggest, long-eared hedgehogs (Hemiechinus and Paraechinus genera) have larger ears and auditory bullae than Erinaceus species (Erinaceus - (Genus)). This is believed to be associated with more sensitive hearing in the former group although this has not been proven to date.(B228.2.w2)
  • The hedgehog snout is long and narrow with a smooth moist black rhinarium (tip of the nose) and a few long whiskers. (B52, B228.2.w2, B255.2.w2, B258.w2, B285.w1, D30)
    • The nose is normally moist and dripping due to respiratory secretions which keep the sensitive respiratory mucosa from becoming dry. (B291.12.w12)
    • The olfactory lobes of the hedgehog brain are particularly well developed, reflecting the importance of the sense of smell in this species. (B258.w2, B228.2.w2, B285.w1)
  • The vomeronasal organ (or Jacobson's organ) is well developed in the hedgehog, consisting of paired blind ending diverticulae which communicate through ducts to both the mouth and nasal chambers.(B228.2.w2) Whilst function of this organ is associated with sexual activity and the characteristic 'flehmen' response in ungulates and many carnivores, its role or function in the hedgehog remains unclear. However, the vomeronasal organ has been observed to be involved with self-anointing behaviour. (B228.2.w2) 

Details of Bone Structure (Osteology)

  • The neck is short. (B258.w2); the short length of the hedgehog neck may be an adaptation facilitating its ability to roll into a tight ball as part of its defence mechanism. (B228.1.w1, B254.7.w7)
  • The hedgehog skull is strong and broad (B254.7.w7); the zygomatic arches are robust and well developed. (B142, B228.1.w1, B258.w2)
  • The condylo-basalar length of the skull in the West European hedgehog (Erinaceus europaeus) and East European hedgehog (Erinaceus concolor) has been reported to be within the range 55-60 mm in a number of studies (B228.1.w1); 40-58 mm.(B142)
  • Variation with geographical region is seen between the degree to which processes of the premaxillary and frontal bones of the skull approach one another. (B142)
  • Skull morphology facilitating identification: tympanic bullae incomplete, sagittal crest extending forward to the level of the caudal end of the frontal bones. (B268)
  • Skull morphology and dimensions can be used to differentiate between the West European hedgehog (Erinaceus europaeus) and East European hedgehog (Erinaceus concolor); the caudal border of the maxilla extends behind the lacrimal duct opening and is proportionately longer in the latter species. (B228.1.w1)
Neonate / Young SUMMARY: Hoglet neonates are born with their ears sealed closed.
  • Hoglet neonates are born with their ears sealed closed. (B142, B228.8.w8, B254.14.w14, B260.6.w6, B261)

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Dentition

Adult SUMMARY: The adult dentition includes a total of 36 teeth, dental formula I 3/2, C 1/1, P 3/2, M 3/3. The deciduous dentition includes 24 teeth; these are shed by 3-4 months of age. Dental abnormalities are not uncommon in Britain and may be particularly common in the population in New Zealand.
  • Dental formula 3.1.3.3/2.1.2.3 (i.e. I 3/2, C 1/1, P 3/2. M 3/3); total 36 teeth. (B142, B258.w2, B289.3.w3)
  • Deciduous dentition consists of 24 teeth.
  • The deciduous dentition is shed by three to four months of age. (B228.1.w1, B254.7.w7)
  • The deciduous dentition does not include molars. (B228.1.w1)
  • Complete adult dentition in the hedgehog is present by the end of the first year of life. (B228.2.w2)
  • The large lower central incisors of the hedgehog are adapted for picking up prey. They are positioned facing forward not upwards and do not form a biting edge with the upper dental arcade. Consequently the bite of the hedgehog is not very painful. (B254.7.w7)
  • Lower incisors fit between large caniniform upper incisors, while second and third upper incisors resemble premolars. (B142)
  • The true canines are small and are the first teeth on the maxilla which have two roots. (B228.1.w1, B260.1.w1)
  • The third upper incisor has a single tooth root. (B268)
  • The rows of teeth are continuous in the hedgehog with no enlargement of the canines. (B142)
  • Premolars have sharp crown cusps adapted to crunching the hedgehog diet. (B260.1.w1)
  • All erinaceid species (Erinaceidae - Hedgehogs, moonrats (Family)) have a characteristic appearance to their first premolar. From the occlusal view, the tooth has a four-cornered appearance (paracone, protocone, hypocone, metacone). The tooth roots on the lingual side of the tooth are fused whilst the roots on the buccal side remain separate. (B228.1.w1)
  • The molars and final premolar are broad with 'blunt tubercles'. (B258.w2)
  • A shearing action exists between the third upper premolar against the first lower molar which mimics the action of the carnassial tooth in carnivores (Carnivora - Carnivores (Order)). (B228.1.w1)
  • Estimation of hedgehog age using timings of dental eruption is not thought to be accurate although teeth which are unerupted confirm that the individual is juvenile. (B228.9.w9)
  • Studies have used the degree of enamel wear in the dentition to allocate age-rankings within samples of adult hedgehog. (B228.9.w9)
  • Tooth wear (dental attrition) often occurs as a result of feeding on a 'gritty' diet such as earthworms (Lumbricus terrestris). (B254.7.w7) Variation is frequently seen in hedgehog dentition. It is estimated that 10% of individuals may have dental or skull anomalies in contrast to the typical pattern.(B260.1.w1)
  • Dental anomalies have been frequently reported in a number of Erinaceus species (Erinaceus - (Genus)). (B228.1.w1) 
    • Dental abnormalities, generally involving the incisors or premolars (deficiency or faulty eruption) is recorded as being common in Erinaceus europaeus from New Zealand (present in 39/77 individuals), while abnormalities, usually involving the second premolar, were seen also in 4/24 individuals from Britain. (J9.202.w1)
    • Studies of 90 hedgehog skulls collected mainly in the Wairarapa, New Zealand, in 1994 found a high proportion of individuals to have dental abnormalities including 46% with missing premolars, 30% with absent or rudimentary incisors and 3% with absent molars. (J190.31.w1)
    • Individual variations in the total number of teeth, persistent deciduous teeth and teeth with double crowns are common findings. (B291.12.w12)
Neonate / Young
  • --

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Eyes

Adult SUMMARY: The eyes are bright black and of moderate size. They are neither enlarged for acute nocturnal vision nor reduced in size. They are normally somewhat prominent.
  • Hedgehogs eyes are of a moderate size. (B228.2.w2)
  • "The black bright eyes are relatively large and somewhat prominent." (B258.w2)
  • Hedgehog eyes are vulnerable to trauma as they move through low level vegetation. (B228.2.w2)
  • Radio-tracking of an individual male hedgehog with severely compromised vision showed that it was able to run a "normal life" although it was observed to "blunder about and often ran into things." (B228.2.w2)
  • Analysis of the dry weight of hedgehog lenses from fresh post mortem material has been performed as a technique for hedgehog age estimation since lens weight increases throughout life. However this method is not though to be widely applicable because of the need for fresh and dead material. (B228.9.w9)
  • The retina contains only rods however about 3.75% of these have nucleuses of cones; these may be responsible for the hedgehog being able to distinguish between colours. (B258.w2)
Neonate / Young SUMMARY: Hoglet neonates are born with their eyes sealed closed.
  • Hoglet neonates are born with their eyes sealed closed. (B142, B228.8.w8, B254.14.w14, B260.6.w6, B261)

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Authors & Referees

Authors Becki Lawson (V.w26); Debra Bourne (V.w5)
Referee Suzanne I. Boardman (V.w6); Nigel Reeve (V.w57)

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