3BS 



MONOTREMATA. 



Fig. 187. 



Thoracic and abdominal viscera, Ornithorhynchus. 



(Meckel.) 



Echidna is unprovided with teeth; but the 

 palate is armed with six or seven transverse 

 rows of strong, sharp, but short retroverted 

 spines. The tongue is long and slender as in 

 the true Anteaters ; its dorsum is broad, flat, 

 callous, and beset with hard papilla, and the 

 insects are doubtless crushed and lacerated 

 between the?e and the pa'atal spines. As, how- 

 ever, the food undergoes less comminution in 

 the mouth of this Monotreme than in that of the 

 Ornithorhynchus, the pharynx and oesophagus 

 are wider, and a dense epithelium lines the 

 inner surface of the latter tube, and is conti- 

 nued over the capacious stomach to the py- 

 lorus, near which orifice it is developed into 

 numerous horny and sharp papillae. The sub- 

 jacent mucous membrane is smooth; the tunics 

 of the stomach are very thin, except at the 

 pylorus, which forms a prominent protuberance 

 in the duodenum. The intestinal canal of the 

 Echidna is seven times the length of the bodv; 

 the mucous membrane is not raised into val- 



vular folds ; a small vermiform and glandular 

 ccecum divides the small from the large intes- 

 tines ; the rectum terminates as in the Ornitho- 

 rhynchus. 



Salivary glands. There appears to be no 

 parotid gland in the Echidna, and it is doubt- 

 ful whether the thin flat stratum of glandular 

 substance (Jig. 180, ), which extends from 

 the meatus auditorius to the check-pouch in 

 the Ornithorhynchus, can be so regarded. The 

 submaxillary gland (Jig. 180, JD) is a mode- 

 rately-sized, oval, compact body, situated be- 

 hind and below the meatus auditorius; it mea- 

 sured five lines in the long diameter and four 

 in the short diameter. The duct is very small, 

 scarcely admitting an absorbent injecting pipe ; 

 it passes under the omo-mylo-hyoideus(10),and 

 then, contrary to the usual mode, begins to be 

 disposed in a series of about twelve close trans- 

 verse folds, and terminates by a single aperture 

 at the fraenum linguae. 



The submaxillary gland (Jig. 188, 6) is of 

 unusual dimensions in the Echidna, in which 

 it extends from the meatus auditorius along the 

 neck, and upon the anterior part of the thorax : 

 it is a broad, flat, oblong lobulated body, nar- 

 rowest at its anterior extremity, from which the 

 wide duct emerges. When the duct has reached 

 the interspace of the lower jaw it dilates, and 

 then divides into eight or ten undulating 

 branches, which subdivide and ultimately ter- 

 minate by numerous orifices upon the mem- 

 branous floor of the mouth. This modification, 

 which escaped the observation of Cuvier and 

 M. Duvernoy, appears to be unique. The 

 large size of the glands and the mode in which 

 the secretion is spread over the floor of the 

 mouth, relate to the lubrification of the long, 

 slender, and extensible tongue, and to its fit- 

 ness as an instrument for obtaining the insect 

 food of the Echidna. 



The liver (Jig. 187, r, r) closely retains the 

 mammalian type of the organ in both Mono- 

 tremes. Four lobes may be distinguished in 

 the Echidna: the principal or cystic lobe re- 

 ceives the suspensory ligament in a fissure; the 

 large gall-bladder is placed a little to the right; 

 the left lobe occupies the left hypochondrium ; 

 the Spigelian lobule is of moderate size; it is 

 an appendage of the right lobe. The liver pre- 

 sents nearly the same form in the Ornithorhyn- 

 chus, which has likewise a large gall-bladder 

 (fig. 187, *) 



There are three hepatic ducts in the Echidna 

 which join the cystic, and the common canal 

 terminates in the duodenum rather more than 

 an inch from the pylorus. In the Ornithorhyn- 

 chus the two chief hepatic ducts join the cystic 

 near the neck of the bladder; the third hepatic 

 joins a more distant part of the cystic; the 

 ductus choledochus receives the pancreatic 

 duct about nine lines before its termination, as 

 in the Marsupials, where its coats are thickened 

 and glandular, and opens into the duodenum 

 about eight lines from the pylorus. 



The pancreas in the Ornithorhynchus is a thin 

 lobulated gland bent upon itself; the left and 

 larger portion descends by the side of the left 



