CHAP, xi SKULL 489 



b. sph. basisphenoid ; cond. condyle of lower jaw ; [cor. coronoid process ; 

 fr. frontal ; int. pa. interparietal ; ju. jugal ; Icr. lacrymal ; m. molars ; max. 

 maxilla ; nas. nasal ; oc. c. occipital condyle ; opt.fo. optic foramen ; o. sph. 

 orbitosphenoid ; 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. premaxilla ; peri, periotic ; pt. pterygoid ; 

 p. t.sq. post-tympanic process of squamosal ; .y. oc. supraoccipital ; sph. f. sphen- 

 oidal fissure ; sq. squamosal ; ty.bul. tympanic bulla ; vo. vomer ; zyg. max. 

 zygomatic process of maxilla. (From Parker and Haswell's Zoology.} 



The upper jaw forms part of the facial region, which 

 encloses the olfactory chambers, and the lower jaw, consist- 

 ing 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, hy). 



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

 arranged in three rings or segments, the middle and pos- 

 terior of which are separated by the auditory capsules (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 basiocdpital (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 exoccipital (e. oc) 

 bound the foramen magnum at the sides, and form the 

 upper part of the occipital condyles : each is produced 

 downwards into a paroccipital process (par. oc) which fits 

 closely against the posterior surface of a swollen bone (ty. but) 

 to be described presently, which is produced into a tube 

 surrounding the auditory aperture (aud. me). The occipital 



1 In the following description, the investing bones are distinguished 

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



