2 



PltOFS. B. L. BHATIA AND BAINI PRASUAD ON THE 



the skulls of several Indian species including R. tigrina, but the 

 account of the latter is incomplete and suffers through having 

 been drawn up from the study of a single specimen. Both the 

 published description and the plate are inaccurate in several 

 important respects, and therefore it was considered desirable to 

 work out in detail the anatomy of the skull of this common 

 Indian frog, and to correct the errors which have crept into the 

 otherwise excellent account given by him. For this purpose the 

 authors have prepared a large series of fresh skulls, and examined 

 them both in the wet and the dry condition. This has been 

 supplemented by an examination of the large number of skulls of 

 this type which are used for study by the students working in 

 the Government College laboratory. 



The Cranium. 



The skull in this frog is very much larger than in the two 

 common European species. An average-sized adult skull measured 

 40 mm. in the antero-posterior and 37 mm. in the transverse 

 direction, while one of the largest measured 45 mm. in the longi- 

 tudinal and 48 mm. in the transverse direction. The cranium, 

 which is wide behind, narrows somewhat anteriorly. The superior 

 surface is markedly arched, its most prominent point being a 

 little in front of the occipital region. All the bones associated 

 with the cranium, both investing and replacing, show a marked 

 development; thus the original cartilaginous structure has been 

 considerably reduced. As remarked by Parker (4), R. tigrina 

 presents one of the most perfect examples of Batrachian cranial 

 architecture. 



The Bones of the Cranium. 



The Exocc'qrital bones (text-figs. 1-4, eo.) bounding the foramen 

 magnum meet each other in the middle line ventral ly, and leave 

 only a very small V-shaped area of unossified original cartilage 

 between their dorsal ends (all that is left uncovered of the 

 original tectum synoticum). The tectum synoticum never reaches 

 the superior border of the foramen magnum, and in the skull of 

 older specimens this little area also becomes ossified. The two 

 bones are seen meeting each other and the slight median pro- 

 jection on the posterior border of the fronto-parietals. In 

 conformity with the great strength and massive proportions of 

 this frog, the occipital condyles are large and are well seen in 

 both dorsal and ventral views of the skull (text-figs. 1-4). 

 Laterally, where the exoccipital meets the prootic it presents a 

 prominent bony ridge (processus mastoideus), there being a thin 

 strip of cartilage between the two bones in the young specimen 

 only. 



The Prootic bones (text-figs. 1 k 7, po.) form a considerable 

 portion of the roof and anterior wall of the auditory capsule, and 

 extend forwards to form a portion of the inner wall of the orbit. 

 Dorsally each presents a quadrilateral area (vide text-fig. 1) 



