17(5 



ZOOLOGY 



SECT. 



Tt.Sp 



h.r 



Tt.Ct 



nch 



nch.sh 



notochord with cartilaginous arches. In Chimsera there are 

 calcined rings (Fig. 800, c. r.) embedded in the sheath of the 

 notochord. The anterior neural arches are fused to form a 

 high, compressed, vertical plate, to which the first dorsal fin 

 is articulated. The cranium (Figs. 801 and 802) has a very 

 characteristic form, largely owing to the compression of the 

 region between and in front of the large orbits, which are 

 separated from the cranial cavity by membrane only in Callo- 



rhynchus (Fig. 802, or.) ; in 

 Chimsera they lie above the 

 level of the cranial cavity 

 and are separated from one 

 another by a median vertical 

 partition of fibrous tissue 

 (Fig. 801, i.o.8). At first 

 sight the palato-quadrate, 

 or primary upper jaw, ap- 

 pears to be absent, but a 

 little consideration shows 

 it to be represented by a 

 triangular plate (pal. qu.) 

 which extends downwards 

 and outwards from each 

 side of the cranium and 

 presents at its apex a facet 

 for the articulation of the 

 mandible. The palato-quad- 

 rate is therefore fused with 

 the cranium and furnishes 

 the sole support for the lower 

 jaw ; in a word, the skull 

 is autostylic. The pituitary 

 fossa (Fig. 802, s. t.) is very 

 deep and inclined back- 

 wards ; on the ventral sur- 

 face of the basis cranii is a 

 pit (pt.) for the extra-cranial 



portion of the pituitary body. The posterior portion of the cranial 

 cavity is very high ; the anterior part containing most of the 

 fore-brain is low and tunnel-like, and has above it a cavity of 

 almost equal size (Nv. 5 o'.) for the ophthalmic branches of the fifth 

 nerves. The greater part of the membranous labyrinth is lodged 

 in a series of pits on the side- walls of the cranium (a. s..,/?.s.c.), and 

 is separated from the brain by membrane only. The occipital region 

 articulates with the vertebral column by a single saddle-shaped 

 surface or condyle (pc. en.). There is a great development of labial 

 cartilages, particularly noticeable being a large plate which, in 



inl 



n.ct 



\--C.7* 



\-h.r 



FIG. 800. Chimsera monstrosa. A, transverse 

 section of vertebral column ; B, lateral view of 

 the same. c. r. calcified ring ; h. r. haemal ridge ; 

 int. intercalary piece ; n. a. neural arch ; nch. 

 position of iiotochordal tissue ; nch. sh. sheath of 

 notochord ; n. sp. neural spine. (After Haasse.) 



