394 



MONOTREMATA. 



The ovaria correspond in situation and sur- 

 rounding attachments with the testes in the 

 male ; and the oviducts and uteri exhibit in 

 their closely convoluted disposition an analogy 

 with the long epididymis or vas deferens. 



The left ovary (Jig. \9\,f) is an irregular, 

 semi-elliptical, flattened body, with a wrinkled 

 and slightly granulated surface in the unexcited 

 state; but thicker, and with the surface studded 

 by elevations formed by the ovisacs in different 

 stages of development at the season of sexual 

 excitement. At this period I have usually 

 found two ovisacs, as in the figure, which are 

 conspicuously larger than the rest, and present- 

 ing each a diameter of about two lines. The 

 right ovary (_/') is a narrow, thin, generally 

 elongated body ; sometimes broader, with a 

 finely granulated surface. It is often scarcely 

 to be distinguished from the ovarian ligament 

 to which it is attached. This ligament (i, i) 

 arises from the posterior parietes of the abdo- 

 men, behind and a little on the outer side of 

 the kidney, and passes along tlie edge of the 

 broad ligament to the fallopian extremity of the 

 oviduct, where it divides into two; one portion 

 is attached to the side of the ovary, the other to 

 the posterior margin of the fallopian orifice: 

 after a course of an inch they again unite, and 

 the ligament is continued along the anterior 

 part of the uterus to its cervix, where it is in- 

 sensibly lost. The two separated portions of 

 the ligament support a large pouch of perito- 

 neum which forms the ovarian capsule ; the 

 wide anterior orifice of the oviduct is also, by 

 means of this ligament, prevented from being 

 drawn away from the ovary. 



The efferent tube of the ovarian products is 

 present on both sides of the body, and is divi- 

 sible into an oviduct, or fallopian tube, (</',) 

 and an uterus (d}. The size of the latter is 

 nearly equal on both sides, but the right ovi- 

 duct is much shorter than the left, and corre- 

 sponds with the abortive condition of the ovary. 

 The external serous coat of the oviduct is 

 loosely connected to the muscular coat by fila- 

 mentary processes of cellular membrane, among 

 which numerous tortuous vessels ramify. The 

 muscular coat is thin and compact, and is most 

 readily demonstrable in the uterus. The mu- 

 cous coat is thin and smooth in the oviduct; 

 it is thick, soft, plicated, but not villous, in 

 the uterus. 



The left uterus in a female with a large 

 ovary, shot in the month of September, was two 

 inches long, from four to five lines in diameter, 

 and about a line thick in its parietes ; it be- 

 came suddenly contracted and thinner in its 

 coats to form the oviduct, which presented a 

 diameter of about two lines, slightly enlarging 

 to within an inch of the extremity, which forms 

 a wide membranous pouch, (d",) opening into 

 the capsule of the ovary by an oblong orifice or 

 slit (e) of eight lines in extent. The edges of 

 this orifice were entire, as in the oviducts of 

 Reptiles, not indented as in the fimbriated ex- 

 tremity of the Fallopian tube in ordinary qua- 

 drupeds. The entire length of the oviduct 

 and uterine tube, when detached from their con- 

 nections with the mesometry, was nine inches. 



The right uterus and oviduct of the same speci- 

 men exhibited similar differences in diameter 

 and structure, but was shelter, measuring only 

 six inches in length. 



In a specimen with a slightly developed 

 ovary, killed by Mr. Bell in April, the uteri 

 were not much wider than the oviducts, and not 

 thicker in their coats; the entire tubes were 

 much less in all their dimensions than those 

 just described. 



In the specimen above described with the 

 large ovary, the thickened parietes of the first 

 portion of the uterine tube depended chiefly on 

 an increase of the inner membrane, which pre- 

 sents in a high degree the character of a se- 

 creting surface. This membrane at the cervix 

 uteri presented in all the specimens many 

 deep and close-set furrows, which, as the canal 

 grew wider, were gradually lost, and the surface 

 became more or less smooth in the different 

 specimens, being most irregular in the speci- 

 men with the largest ovary. In the oviduct, 

 the inner surface is at first smooth after leaving 

 the uterus, but beyond that becomes finely re- 

 ticulate, and in the terminal dilated part be- 

 comes again smooth. The cervix uteri makes 

 a valvular projection analogous to an os tincae 

 on each side of the commencement of the uro- 

 genital canal, just beyond the orifice of the 

 urinary bladder. There are two orifices on 

 each of these prominences; the lower one is the 

 termination of the ureter, and a bristle is repre- 

 sented as passing through it in Jig. 191 ; the 

 upper or anterior orifice is the os uteri, m. 



In young or virgin Ornithorhynchi this ori- 

 fice forms scarcely any projection into the uro- 

 genital canal, and it is divided by a narrow 

 septum, or hymen.* 



The uro-genital canal (c) is one inch and a 

 half long, and three or four lines in diameter, 

 but capable of being dilated to as great an 

 extent probably as the pelvis will admit of; 

 the diameter of the bony passage being seven- 

 tenths of an inch. It is invested with a mus- 

 cular coat, the external fibres of which are 

 longitudinal, the internal circular. The inner 

 membrane of this part is disposed in longi- 

 tudinal rugae more or less marked, but pre- 

 sents as little the character of a secreting mem- 

 brane as that of the vestibule, being smooth 

 and shining ; the orifices of a few minute 

 follicles are situated in the interstices of the 

 rugae near the orifice of the urinary bladder. 



It is this division only of the passage from 

 the uterus which is situated within the pelvis, 

 the vestibule being produced beyond it, and 

 the common outlet being in consequence situ- 

 ated at a considerable distance from the outlet 

 of the pelvis.! 



If the Ornithorhynchus were oviparous, its 

 eggs must be disproportionately small compared 

 with those of birds, in order to pass through 

 the unyielding pelvis, unless the albumen and 

 shell were subsequently added to the yolk in the 



* Geoffroy, Mcmoires du Museum, torn. xv. 

 p. 32. 



f In this structure, as well as in its aquatic life, 

 the Ornithorhynchus resembles the Beaver. 



