LESS. XXIX 



ENTERIC CANAL 381 



In the skeleton the cartilaginous parts are dotted, the bony ends of 

 the vertebrae black, en, centra ; «. a, neural arches ; h. a, hjemal 

 arches ; cr, cranium ; r, rostrum ; u. j, upper jaw : /. j, lower jaw ; 

 b. hy, basi-hyal, supporting tongue {tng) ; b. br, basi-branchial ; pet. a, 

 pectoral arch ; pv. a, pelvic arch. The front part of the cranium is 

 roofed by a membranous fontanelle (/<?«). 



The enteric canal with the liver (/. Ir, r. Ir), &c, has been displaced 

 downwards, and the oral cavity and pharynx {ph), part of the intestine 

 {mi), and the cloaca (cl) have been opened, sp, spiracle ; ;. br. a>-i. br. ofi, 

 internal branchial apertures ; cd. st, cardiac, and pyl. st, pyloric portions 

 of stomach ; sp. vl, spiral valve of intestine {int) ; /. /r, left, and r. ir, 

 right lobe of liver ; pan, pancreas ; spl, spleen ; ret. gl, rectal gland ; 

 nies, mesentery. 



The heart consists of sinus venosus (j. v), auricle (««), ventricle {»), 

 and conus arteriosus (c art) : the latter gives off the ventral aorta {v. ao) 

 from which are seen to arise the afferent branchial arteries of the right 

 side. The dorsal aorta (rf. ao) receives anteriorly the efferent branchial 

 arteries, and posteriorly becomes the caudal artery {cd. a), lying above 

 the caudal vein {cd. v). 



The spinal cord {sp. cd) passes in front into tlie brain, which consists 

 of medulla oblongata (wft/. obi), cerebellum {crb), optic lobes (<j//. /), dien- 

 cephalon {dien), proscephalon {prs), and olfactory lobes {olf. I). To the 

 diencephalon are attached the pineal {pin) and pituitary {pty) bodies. 



The left kidney {kd) opens by the ureter {ur) into the ufinogenital 

 sinus (m. g. s) which discharges into the cloaca. The left spermary {ts) 

 is connected with the epididymis {epid) from which the vas deferens 

 {v. def) passes backwards, dilates into the vesicula seminalis {vs. sent) 

 and opens into the urinogenital sinus, with which is also connected the 

 sperm-sac {sp. s). Attached to the fold of peritoneum supporting the 

 liver is a small tube (/. n. d) representing the oviduct of the female. 



The mouth (Figs, 99, Mth and 103) leads into an oral 

 cavity (Or. cav), which passes insensibly into the throat or 

 pharynx {ph), a division of the enteric canal distinguished 

 by having its walls perforated by five pairs of slits, the in- 

 ternal branchial apertures (i. br. a 1-5) as well as by the inner 

 opening of the spiracle {sp). The pharynx is continued by a 

 short gullet {gut) into a capacious U-shaped stomach consist- 

 ing of a wide cardiac division {cd. st) and a narrow pyloric 

 {pyl. st) division. The pyloric division communicates by a 

 narrow valvular aperture with the intestine {int), a wide, 

 nearly straight tube having its lining membrane produced 

 into a spiral fold, the spiral valve {sp. vl), which practically 



