638 ANATOMY OF VERTEBRATES. 



§ 368. Opening on the limbs. — In certain Bats (Emballonura, 

 e.g.) a glandular cutaneous sac, exuding a reddish mal-odorous 

 secretion, opens upon the anterior border of the wing, near the 

 head of the humerus. In Saccopteryx (at least in the male) a 

 larger sac, with a plicate internal surface situated on the under 

 part of the wing, near the ulna, opens by a fissure on the upper 

 surface of the limb. 



In the one-horned Rhinoceros (Rh. indicus, and probably in 

 other species) there is a glandular orifice at the back part of each 

 foot, situated about three inches above the callous sole : it is con- 

 cealed in the middle of the transverse fold that runs parallel to 

 the interspace between the carpus and metacarpus, and between 

 the tarsus and metatarsus. The gland is of a compressed ovate 

 figure, measuring one inch and a half in length, and one inch in 

 breadth : it is hollow, with parietes from two to three lines in 

 thickness, consisting of a compact congeries of follicles, sur- 

 rounded externally by a muscular and 



499 • 



tendinous capsule. The external orifice 

 may be expanded to a width of eight 

 lines. * 



In most bisulcate Ungulates a similar 

 gland exudes its lubricating sebaceous 

 secretion from an orifice at the upper 

 and fore part of the cleft between the 

 principal hoofs. In the sheep, fig. 499, 

 the gland is elongate and bent forward 

 at an acute angle upon its duct, (indi- 

 cated by the bristle in the figure and 

 preparation). These post-digital and 



Iuteruugulatc gland, Sheep.2 ' , t • , i i i • l , i 



mterdigital glands, in ungulate quadru- 

 peds, seem to relate to lubricating or greasing the hoofs. 



The most remarkable of the ' peculiar glands ' in the Mamma- 

 lian class, and one that relates most closely to sex, is that which 

 in the mature male Monotremes sends its duct to terminate in 

 the hollow spur projecting from the heel. The character is not 

 manifested in the young animal. A small spur concealed in a 

 cavity or socket of the integument covering the heel, the bottom 

 of which closely adheres to the accessory tarsal ossicle, exists in 

 the immature of both sexes. 3 As the young animal advances to 

 maturity the cutaneous socket increases in width and depth in the 

 female, but without any corresponding growth of the rudimentary 



1 v", p. 34, pi. ix. figs. 1 and 2. 2 xx. vol. Hi. No. 2152 n. 



3 A magnified view of the part in the young male is given in lxxviii'. pi. 32, figs. 1 & o. 



