in the Bones of some Frogs and Fishes. 385 



form, from the middle of the bone upwards, one high ridge, 

 which is lost before reaching the caput humeri. To which of 

 the South American species is this bone to be referred ? A 

 similar structure of the humerus has only been known in Cysti- 

 (jnathus ocellatus, Spix* has described this species under a 

 new name, C. pachypus. Without knowing the osteological 

 peculiarity, he chose this name from the externally visible 

 strength of the upper arm ; and he was well aware of the fact of 

 a sexual difference, neglected by all subsequent naturalists. He 

 observes, "humero maris intumido,^' and *^foemina differt amare 

 femore pedis anterioris non incrassato/^ Prof. Stannius f first 

 mentions the internal structure in these words : — '^ In C.pachypus 

 the humerus is peculiarly developed in breadth, becoming a 

 nearly flat bone." We find it more accurately described by Prof. 

 Owen J. In this species, namely (PI. XV. fig. G.), the two hinder 

 ridges are enormous, and form a broad crescent-shaped plate, 

 the breadth of which exceeds twice that of the central bone ; 

 there is, moreover, a fourth ridge at the hinder side of the bone, 

 convergent with the other one descending from the caput 

 humeri. A comparison of several skeletons has now shown me 

 that this structure is peculiar to the male only, whilst the bone of 

 the female is framed as in other frogs, viz. exhibiting the spina 

 tuberculi majoris alone. It is evident at the first glance that our 

 fossil does not represent a bone of the latter species, whilst it 

 perfectly agrees with the humerus of a male C. labijrinthicus 

 (fig, E.), with some slight differences of size, and perhaps of age. 

 In the female of C. labijrinthicus (fig. F.) the humerus is 

 formed as in C ocellatus. It must be mentioned, that neither 

 in Ceratophrys nor in the Australian Cystignathidce does a similar 

 osteological difference of the sexes exist. The physiological 

 relation of this structure to the process of propagation is as clear 

 as the development of the rudimentary thumb and of the second 

 metacarpal bone in the males of many xVnura. The second meta- 

 carpal bone has, besides, in several species of Cijstignathus, an 

 external acute conical spur. 



Such sexual differences, conspicuous in parts of the skeleton, 

 occur in all the classes of Vertebrata, and certainly are of great 

 importance to the palseontologist. Some years ago, I pointed out 

 that the thick ray in the ventral fins of the Tench {Tinea vulgaris) 

 is a sexual peculiarity of the male, not present in the female §, — 

 an observation which has been latterly adopted and confirmed by 

 Heckel||. I was not then aware, nor has it been observed by 



* Spec. nov. Test. Ran. p. 26. 



t Stannius iind Siebold, Vergl. Anat. Reptil. p. 143. nota 1. 

 X Osteol. Catal. i. p. 120. § Neckartische, p. 51. 



II Ileckel und Kner, Siisswasserfische Oestr. p. 77 > 

 Ann, §• Mag, K Hist, Ser. 3. Vol, iii. 35 



