ANATOMY OF RA-XA TIGRIXA. 609 



The coracoids, while having the normal shape and ti-ansvei'se 

 position, do 7iot meet in a median epicoracoidcd cartilage hut 

 overlap each other in the middle line. At first sight it appears 

 that there is merely an uneven suture, such as is seen between 

 tlie epicoracoid cartilages of an immature Rana temporaria, but 

 a closer examination reveals the existence of a definite overlap 

 {rf. text-fig. 3). 



It difi:ers from the overlap of the arciferous condition in that 

 the epicoracoidal cartilage is completely calcified in the adult 

 and that the coraeoid comes, at its antero-mesial border, into 

 contact with the clavicle upon the ventral surface. There is, I 

 believe, synostosis between the two coracoids, for there appears 

 to be no freedom of movement. 



The direction of the overlap, in the specimen figured, resembles 

 that prevailing in the Arcifeiu, the right coraeoid lying ventral to 

 the left, but the opposite condition is met with not infrequently *. 



Dorsally the pre-coracoid cartilage is seen. It appears to be 

 calcified, and separates, somewhat widely, the clavicle from the 

 coraeoid. 



The bony style of the omosternum is also peculiar (amongst 

 Ranidaj) in being bifid posteriorly. The diverging processes 

 meet corresponding elevations upon the clavicles, and the small 

 space between the three bones is filled, in life, by a delicate 

 membrane. 



The Tenth Spinal Nerve. 



Correlated with the minute size, or the absence, of the foramina 

 in the coccyx, the tenth pair of sj^inal nerves are, in Rana tigrina, 

 either extremely delicate or, more often, altogether absent. 

 When present, they seem invariably to pass dorsally from their 

 exits, lying in that small groove in the coccyx, to which reference 

 has been made. In this disposition, therefore, this nerve differs 

 considerably from the corresponding structure in R. temporaria, 

 in which it passes ventrally after leaving its foramen. In the 

 Bull-frog the nerve, even if present, is hidden from view in a 

 dissection made, in the usual manner, from the ventral surface. 

 It never, in this species, I believe, makes any contribution to 

 the sciatic plexus, nor have I been able to demonstrate any 

 sympathetic ganglion related to it. 



Literature. 



'11. Beddabd, F. E. — "Contributions to the Anatomy of the 



Anura." Proc. Zool. Soc. 1911, p. 393. 

 '97. BouLENGER, G. A. — The Tailless Batrachians of Europe. 



Yol. I. Ray Society. 1897. 

 '02. Howes, G. B. — An Atlas of Zootomy. London, 1902. 

 '15. NiCHOLLs, G. E.— "A Note on the TJrostyle {Os Coccy- 



geimi) of the Anurous Amphibia." Proc. Zool. Soc. 



1915, p. 239. 



* Beddard ('11, p. 396) lias pointed out that variation in this arraugtmeut is also 

 occasionally uiicouutered in Mefjalophri/s fcce. 



