CHAP, xi SKULL 489 



parietal ; i. o. /. infraerbital foramen for passage of the maxillary division of the 

 trigeminal nerve ; ju. jugal ; Icr. lacr>-mal ; Ur. for. lacrymal foramen ; m. 

 molars ; max. maxilla ; IMS. nasal ; of. c. occipital condyle ; opt. fo. optic 

 foramen ; o. spit, orbitospbenoid ; pa. parietal ; pal. palatine ; pm. premolars ; 

 pal. max. palatine process of maxilla ; par. oc. paroccipital process of exoccipital ; 

 pal. p. max. palatine process of premaxilla ; p. max. premaxiUa ; peri, periotfc ; 

 pit. for. pituitary foramen ; pt. pterygoid : p. t. sq. post-tympanic process of 

 squamosal ; s. oc. supraoccipital ; sph. f. sphenoidal fissure ; w. squamosal ; ty. 

 bui. tympanic bulla ; no. vomer ; zyg. mzx. zygoma tic process of maxilla ; V. 

 mn. foramen for mandibular division of trigeminal nerve ; VII. for facial nerve ; 

 IX. X. XI. for gkjssopharyngeal, vagus, and spinal accessory ; XII. for hypo- 

 glossal. (From Parker and Haswell's Zoology.) 



The upper jaw forms part of the facial region, which 

 encloses the olfactory chambers ; and the lower jaw, con- 

 sisting of a single bone on either side, articulates directly 

 with the sides of the cranium without the intervention 

 of a hyomandibular as in the dogfish (p. 438) or of a 

 quadrate cartilage as in the frog (p. 44). The rest of 

 the visceral portion of the skull, representing the hyoid 

 and first branchial arch, forms the so-called hyoid bone 

 which is embedded in the base of the tongue (Fig. 135, 

 ky). 



The bones l which form the walls of the brain-case are 

 arranged in three rings or segments, between the middle 

 and posterior of which are intercalated the auditory cap- 

 sules (Figs. 133 and 132 A, peri). 



The posterior, or occipital segment, consists of three 

 bones, which in the adult become completely united with 

 one another. The lower of these is the basioccipital (b. 

 oc), a flattened bone bounding the foramen magnum 

 below, and forming the hinder part of the base of the 

 skull and the lower part of each occipital condyle (oc. c). 

 The two exoccipitals (e. oc) bound the foramen magnum at 

 the sides, and form the upper part of the occipital con- 

 dyles : each is produced downwards into a paroccipital 

 process (par. oc) which fits closely against the posterior 

 surface of a swollen bone (ty. bid) to be described 

 presently, which is continuous with a tube surrounding 



1 In the following description, the investing bones are dis- 

 tinguished by an asterisk from the replacing bones (see p. 43). 

 PRACT. Zoou. H H 



