PECULIAR GLANDS OF MAMMALIA, 



639 



spur, of which in aged females no trace remains. In the male Or- 

 nithorhynchus the tarsal spur soon begins to rise above the socket, 

 and finally attains a length of ten lines with a basal breadth of five 

 lines, apparently everting the tegumentary socket in the progress 

 of its growth. The spur, fig. 500, e, consists 500 



of a firm semitransparent horn-like sub- 

 stance ; it is conical, slightly bent, and ter- 

 minated by a sharp point ; its base is ex- 

 panded, and notched at the margin for the 

 implantation of the ligaments which connect 

 the spur with the accessory flat tarsal bone 

 (vol. ii. fig. 199 k, d.) The base of the 

 spur is covered by a thin vascular integu- 

 ment. The spur is traversed by a canal 

 which commences at the centre of the base 

 and terminates by a fine longitudinal slit, 

 about one line distant from the point, closely 

 resembling in this respect the canal that tra- 

 verses the poison-fang of the venomous snake. 

 Like that weapon the spur of the male Mo- 

 notreme is subservient to the transmission 

 into the wound it may inflict of the secretion 

 of a peculiar gland. 



This gland, fig. 500, a, is situated at the 

 back part of the thigh, between the femur and 

 the long olecranoid process from the head of 

 the fibula, covered by the integument and 

 the cutaneous muscle. It is triangular, con- 

 vex above, concave below, or toward the leg, 

 from twelve to fourteen lines in length, seven or eight lines broad, 

 and three or four lines thick, with a smooth exterior, invested by 

 a thin capsule, on the removal of which the gland may be divided 

 into a number of small lobes. Its intimate structure, as displayed 

 by a successful injection of mercury, is minutely cellular ; the 

 excretory duct is continued from the concave side of the gland, 

 and small clusters of vesicles are developed from parts of its 

 expanded commencement. The duct, which is about a line in 

 width and with pretty strong tunics, descends straight down the 

 back of the leg, covered by the flexor muscles, to the posterior 

 part of the tarsus, where it suddenly expands into a vesicle, ib. b, 

 applied to the base of the spur, and a minute duct, ib. c, is con- 

 tinued from it into the canal which traverses the spur. 



The tarsal perforated spur and its glandular apparatus are both 



Crural gland and spur, male 

 Ornithorhynchus. lxxxi'. 



