Characteristic features of mammalian skull is discussed below:
1) The mammalian skull is mainly composed of two parts: cranium and mandible.
2) The skull is made of 29 bones of which 8 are cranial bones, 14 are facial bones, 6 auditory bones and 1 hyoid bone.
3) Their skull is dicondylic as each of their exoccipital bears an occipital condyle to articulate with anterior most atlas vertebra.
4) The cranium encloses the brain and thus protects it and so is also called as brain box. It is divisible into three major regions: anterior frontal region, parietal region, and posterior occipital region.
5) The maxillary bone (commonly called cheekbone) fuses with a bone present on the side of the skull and forms an arch called, the zygomatic arch.
6) Chewing food is usually controlled by muscles present between the jaw bone (or mandible) and the zygomatic arch.
7) The anterior part of frontal region consists of six bones: (a) two dorsal frontals, (b) one ventral presphenoid, and (c) two lateral orbitosphenoids.
8) The anterior margin of the cranial cavity is closed by a vertical bone ‘the cribriform plate’.
9) The parietal region of the cranium is present in front of the occipital region. It has a ventral basisphenoid, two dorsal parietal bones and two lateral alisphenoid bones.
10) At the posterior occipital region of the cranium there is a wide opening named foramen magnum, through which the brain emerges out as spinal nerve cord.
11) The mammalian skull generally has three different types of sensory capsules: (a) paired olfactory capsules, (b) paired optic capsules and (c) paired auditory capsules.
12) The mammalian skull has orbital complexes. These are the large circular area that surrounds the eyes of the mammals. Each orbital complex is made of both cranial and facial bones.
Difference between the skull of herbivore and carnivore mammals:
i) The posterior end of the jaw called the angle, which is the bony part present just below the ears of mammals. In herbivores it is expanded and convex. While in carnivores the angle is quite small.
ii) Among the two main jaw-closing muscles: musculus temporalis and musculus masseter. In herbivores the masseter muscle is usually larger and stronger than the temporalis muscle. While in carnivores the temporalis muscle is usually larger and stronger than the masseter muscle.
iii) The facial muscle in herbivore is well developed, while in carnivores it is reduced to allow wide mouth gap.
iv) Herbivorous mammals usually have a large gap between their fore and hind teeth in order to store food while eating. Whereas, carnivorous mammals usually have large sites along the top of their cranium to attach their large jaw muscles and give them strength to chew hard materials such as bones and flesh.
v) Teeth of carnivorous mammals are designed for cutting meat and crushing bone. Their molars are usually pointed and wedge-like. Their incisors are relatively smaller. Many carnivores have large canine teeth which is used for dragging their prey around and gripping it. Insectivores have sharp cusps in order to break the exoskeleton of their prey easily. While, herbivorous mammals have flat teeth which is designed for grinding their food particles and also to perform nonstop chewing.
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