MAMMALIA : PROTOTHERIA. 371 



There are no chordae tendineae, and the musculi papillares are attached to 

 the membrane of the valve, and in Ornithorhynchus even invade its sub- 

 stance, and extend to the auriculo-ventricular ring ; and in this animal a 

 transverse section of the ventricles is remarkably Avian in character *. 

 The thyroid cartilage in the larynx is formed of two separate cartilages, 

 and the cricoid shows traces of its origin from a number of tracheal rings. 

 The rectal and urogenital canals unite in a common cloaca which is closed 

 by a sphincter muscle. The ureters open below the neck of the bladder 

 into the urogenital canal itself. The testes are retained within the abdomen : 

 the left ovary is larger than the right. The vasa deferentia open separately 

 into the urogenital canal, as do the oviducts. The latter have non-fim- 

 briate abdominal apertures, and are dilated towards their lower extremities 

 with a thickened mucous membrane. There is no thickened muscular 

 uterus. The oviducal aperture opens above that of the ureter on a common 

 papilla. The penis is attached to the ventral wall of the cloaca : and 

 consists of two corpora cavernosa. It is perforated by a canal which can 

 be brought into temporary connection with the openings of the vasa defe- 

 rentia. The clitoris is large. The mammary glands are two in number, 

 and their ducts open on an area of the skin which is depressed in Echidna, 

 flat in Ornithorhynchus, The ova are large and meroblastic, and the tunica 

 granulosa of the Graafian follicle consists, as in Sauropsida, of but a single 

 layer of cells. Ornithorhynchus lays its eggs on a rough kind of nest at 

 the bottom of a burrow : Echidna carries them in a marsupial pouch which 

 appears to be developed at stated periods, and to arise in the first instance 

 as two folds, each inclosing a mammary area. The young animal has a 

 knob or caruncle, as in some Aves, on the snout, which probably assists in 

 perforating the tough egg-shell. 



The temperature of the body in Echidna is said to be 28C, in Ornithorhynchus 

 24-8C., by Miklucho-Maclay, Nature, xxxi. 1884-85, p. 809. That of other 

 Mammals, according to J. Davy, is 38-4C. 



Gould, 'Mammals of Australia,' 3 vols. 1845-63. Echidna, Oldfield Thomas, 

 P. Z. S. 1885. Corpus callosum of Echidna, Flower, Ph. Tr. 155, 1865. Eye of 

 Ornithorhynchus, Gunn, Journal of Anat. and Physiol. xviii. 1884. Cochlea of same, 

 Pritchard, Ph. Tr. 172, 1881. Tongue of Ornithorhynchus, Poulton, Q. J. M. xxiii. 

 1883 ; sense organs of bill in do., Id. Proc. Physiol. Soc. in Journal of Physiology, 

 1884, p. xv. Heart, Ray Lankester, P. Z. S. 1882; 1883. Reproductive organs, 

 Martin Saint- Ange, Etudes de Fappareil reproducteur, Paris, 1854. Ovum, Poulton, 

 Q. J. M. xxiv. 1884; of Echidna, Beddard, Proc. Roy. Phys. Soc. Edinburgh, viii. 

 1885; Ramsay, A. N. H. (5) xvi. 1885; Do. and oviparity, Baldwin Spencer, 

 Nature, xxxi. 1884-85. Marsupial ovum, pouch and mammary glands of Echidna, 

 Haacke, P. R. S. xxxviii. 1884-85, cf. von Lendenfeld, Z. A. ix. 1886. 



1 An anterior abdominal or epigastric vein, arising from the bladder and distributed to the left 

 lobe of the liver, has been found in a female Echidna. It may not be a constant structure. Beddard, 

 P. Z. S. 1884. 



B b 2 



