32 



The auditory capsules. Note — 



(a) The periotics, irregularly shaped bones in the side wall of 



the cranium, between the squamosals and the occipital seg- 

 ment, each consisting of a dense petrous portion, and a 

 cancellated mastoid portion with a downwardly directed 

 mastoid process. 



(b) The tympanies, in each of which may be recognised a tubular 



upper portion (the neck or external auditory meatus), and an 

 expanded lower portion (the bulla). 



(0) The auditory ossicles, seen on breaking away the outer wall 



of the tympanic bone. Observe — 



(1) The malleus, with its long process (the manu- 



brium) attached to the tympanic membrane. 



(2) The incus, articulating with the malleus, and 



giving off two processes, the long and short 

 crura. 



(3) The OS orbiculare, a small disc of bone attached to 



the long crus of the incus. 



(4) The stapes, a stirrup-shaped bone articulating 



with th& OS orbicularCj and having its base 

 inserted into the fenestra ovalis. 

 Connected with the auditory capsules are the squamosals, a pair of bony 

 plates in the cranial wall below the parietals, articulating with the' 

 periotics, orbito sphenoids, and ali-sphenoids. Each sends forwards 

 and outwards a stout zygomatic process to articulate with the jugal 

 bone. 

 Eones in connection with the Jaws. 

 (a) The upper jaw. 



(1) The maxillae, a pair of large irregular bones, in each of which 



the following parts may be distinguished : the body or 

 alveolar portion, extending backwards into the front part of 

 the orbit, and inwards to form the transverse palatal process 

 (part of the hard palate) ; the zygomatic process, prolonged 

 upwards into the orbital process, which forms the anterior 

 boundary of the orbit ; the fenestrated facial plate, forming 

 the lateral boundary of the olfactory chamber. 



(2) The pre-maxillse, a pair of bones forming the anterior part 



of the upper jaw, articulating with each other in front and 

 with the maxillsB behind, and each sending a long, slender 

 nasal process backwards between the nasal bone and the 

 maxilla as far as the anterior process of the frontal. 



(3) The pterygoids, a pair of narrow vertical plates of bone 



attached to the skull at the junction of the alisphenoids 

 with the basi-sphenoid. 



(4) The palatines, a pair of nearly vertical plates of bone, articu- 



