{253}[Illustration: FIG. 153.—Dissection of a male Dog-Fish (_Scyllium_). The left side of the body is cut away to the median plane so as to expose the abdominal and pericardial cavities and the neural canal in their whole length. The alimentary canal and the liver have been drawn downwards, and the oral cavity, the pharynx, part of the intestine, and the cloaca have been opened. The cartilaginous parts of the skeleton are dotted, and the calcified portions of the vertebral centra are black. _abd.cav_, Abdominal cavity; _au_, auricle; _b.br_, basi-branchial; _b.hy_, basi-hyal; _c.art_, conus arteriosus; _cd.a_, caudal artery; _cd.st_, cardiac part of the stomach; _cd.v_, caudal vein; _cl_, cloaca; _cn_, centrum; _cr_, cranium; _crb_, cerebellum; _d.ao_, dorsal aorta; _dien_, thalamencephalon; _epid_, epididymis; _fon_, fontanelle; _gul_, oesophagus; _h.a_, haemal arch; _i.br.a^1_-_i.br.a^5_, internal gill-clefts; _int_, intestine; _kd_, kidney; _l.j_, lower jaw; _l.lr_, left lobe of liver; _med.obl_, medulla oblongata; _mes_, mesentery; _n.a_, neural arch; _n.cav_, neural canal; _olf.l_, olfactory lobes; _opt.l_, optic lobes; _pan_, pancreas; _pcd.cav_, pericardial cavity; _pct.a_, pectoral arch; _ph_, pharynx; _pin_, pineal body; _p.n.d_, vestigial Müllerian duct; _prs_, prosencephalon; _pty_, pituitary body; _pv.a_, pelvic arch; _pyl.st_, pyloric portion of the stomach; _r_, rostrum; _r.lr_, right lobe of liver; _rct.gl_, rectal gland; _sp_, spiracle; _sp.cd_, spinal cord; _spl_, spleen; _sp.s_, sperm sac; _sp.vl_, spiral valve; _s.v_, sinus venosus; _tng_, tongue; _ts_, testis; _u.g.s_, urino-genital sinus; _u.j_, upper jaw; _ur_, metanephric duct; _v_, ventricle; _v.ao_, ventral aorta; _v.def_, vas deferens or mesonephric duct; _vs.sem_, vesicula seminalis. (From Wiedersheim, after T. J. Parker.)]