PLATANISTA. 501 



Cuvier, Escliricht and Elower liad formed of its anomalous character, and to establish 

 the position assigned to it by Dr. Gray as a distinct sub-family of the toothed 

 whales, including the genus Inia, and through Pontoporia connected with the true 

 DelpMnid(2. 



Supra-occipital (PL XL, fig. 2). — In the skull (10*75 inches long) of a young 

 male caught in August, and therefore probably only a few months old, this bone is 

 quite distinct from the exoccipital, but confluent at its upper angles with the parietals. 

 The obscure external occipital crest is prolonged downwards, towards the margin of 

 the foramen magnum, terminating in the incision or cleft (fig. 2, cT). There is a 

 slight concavity on the sides of the upper half of the ridge, but the lower half of 

 this surface of the bone is somewhat convex. The upper two-thirds of the internal 

 surface are deeply concave, the lower third almost flat. The former portion is tra- 

 versed by a prominent sharp vertical ridge, with no trace of a groove for the 

 longitudinal sinus, but the transverse ridge shows indications of grooving for the 

 lateral sinus. The sides of the ridge are marked by numerous nutrient foramina, 

 and the fossae themselves by long fine meningeal grooves. The cerebellar fossa is 

 nearly flat in its upper half, but concave above the margin of the foramen magnum. 

 The parietal margin of the bone equals the length of the exoccipital border. 



In another and older male skull, measuring 14 inches in length, the parietal and 

 frontal edges of the supra-occipital are slightly prolonged backwards, with an inward 

 curve in the case of the former and backward curve in the case of the latter, below 

 which there is a considerable concavity. The bone, however, is convex from the 

 parietal to the margin of the foramen magnum, and the feebly-marked vertical ridge 

 has a diminutive tuberosity. The incision at the foramen magnum is closed at the 

 border of the orifice, but an elongated imperfection still exists above this. The fora- 

 men magnum preserves the same form as in the foetal skull. The internal vertical 

 ridge is very sharp. 



In a male skull, adult or nearly so, the occipital region has undergone a 

 remarkable change of form, which is also characteristic of the female. It is oblong 

 and deeply concave between the parietals. This is due to the development of a 

 prominent lambdoidal ridge, turning outwards and downwards in the position of 

 the upper angle of the exoccipital to the base of the zygoma, and to an equally 

 marked sagittal crest. In one adolescent adult, there is a rough nodular tuberosity 

 but no ridge, while in a female of considerable adolescence, so to speak, the occipito- 

 interparietal region is narrower and deeper than in males of apparently nearly the 

 same age, and there is neither a trace of a tuberosity nor of a vertical ridge ; yet, in 

 another example, adult and of the same size, the tuberosity alone is developed. In 

 adult skulls the incision at the foramen magnum disappears. 



Exoccipitals. — In the foetal skull, the line of separation between these bones 

 and the basi-occipital cannot be detected, the exoccipitals being only ossified on a 

 line with the inferior extremities of the facets for the atlas, but anterior to that and 

 between the facets there is a considerable cartilaginous area. Before the facets they 

 are rather deeply concave, but their external surfaces are rather convex, especially 



