. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. MONOTREMATA. 387 cardiac, pulmonic, cesophageal, and gastric nerves. The spinal accessory nerve (jig. 180, c) is thicker than the pneumogastric, and has the usual distribution. The brachial plexus is formed by the five posterior cervical and the first dorsal nerves. The third cervical nerve is shown at g,Jig-180. The median nerve perforates the inner condyle of the humerus. The lumbar plexus is formed by the two posterior dorsal, the two lumbar, and the first sacral nerve. The great ischiadic nerve divides into the peron
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. MONOTREMATA. 387 cardiac, pulmonic, cesophageal, and gastric nerves. The spinal accessory nerve (jig. 180, c) is thicker than the pneumogastric, and has the usual distribution. The brachial plexus is formed by the five posterior cervical and the first dorsal nerves. The third cervical nerve is shown at g,Jig-180. The median nerve perforates the inner condyle of the humerus. The lumbar plexus is formed by the two posterior dorsal, the two lumbar, and the first sacral nerve. The great ischiadic nerve divides into the peroneal and tibial branches before it quits the pelvis. The crural nerve is shown at h (jig. 180). DIGESTIVE SYSTEM. The Ornithorhynchus, which subsists on aquatic insects, larvae, mollusks, and other small invertebrates which conceal themselves in the mud and banks of rivers, is provided with a mouth which most nearly resembles the flat and sensitive bill of a lamellirostral bird. The singularly modified jaw-bones, already de- scribed, are invested by a smooth coriaceous inte- gument, (fig. 173, A, E, a,) devoid of hair, but perforated by innumerable minute foramina. At the base of the jaws this integument is produced into a free fold, which overlaps the hairy covering of the cranium immediately behind it. The integument covering the upper mandible ex- tends beyond the margins of the bone, and forms a tumid, smooth, and highly sensible lip; the narrower and shorter under jaw is more closely invested : the oral or upper sur- face of the lateral part of the under jaw sup- ports a series of about twenty nearly transverse folds, increasing in breadth as they approach the angle of the jaw : the corresponding sur- face of the upper jaw is smooth. The two anterior horny teeth in both jaws are elongated, narrow, with their outer part raised into a trenchant edge in the lower jaw. The two posterior teeth (Jig. 173, h, and F) in both jaws are flat, with two broad and slight excavations, co
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