PLATANISTA. 



451 



tlie nasal cartilage and below the postnodular pad. Mesially there is a strip of 

 septal cartilage. 



rig. 15. 



A vertical section through the head of Platanista rjangetica, slightly to the right of the median line, designed to 

 show the spiracular cavity and sacs, the fibrous blubber of the forehead, interior of brain cavity, and nerves 

 supplying the teeth. The snout is curtailed, and the lower jaw, tongue, &c., have been cut away. Drawn 

 fi-om nature and reduced about ^rd nat. size. 



0, skin of the left side of the orifice of the blow-hole (an arrow is directed downwards through the spiracular 

 cavity, and its point is shown passing into (pn) the posterior nares) ; bl, the coarse fibrous tissue and blubber 

 and fibrous material of the forehead, and which substance reaches quite to the top of the skull ; ca, cartila- 

 ginous piece in the blow-hole ; p, pad, immediately to the inside of the latter ; a Sf i, fibrous elevations or 

 cushions in front wall of spout-hole, and here seen in section ; I, lowermost nasal oac (premaxillary ) ; II, 

 orifice of lateral sac (maxillary), the dotted line signifies its position, otherwise it is bidden in the fleshy 

 substance ; III, narrowed spiral canal which passes partly round [ca) the nasal cartilage and constitutes the 

 small third nasal sac ( = nasof acial) ; s, cartilaginous septum nares ; pmx, premaxillary bone ; mx, maxillary ; 

 f, vomer ; J3, pterygoid ; f, frontal; i«, basi-sphenoid ; io, basi-occipital ; e, occipital condyle ; so, supra-occi- 

 pital ; 5, sphenoidal fissure ; 7, internal auditory foramen ; 8, fissure exit of eighth pair of nerves ; g, condyloid 

 foramen ; m, neck muscles ; n, branches of superior dental nerve. 



Fosterior Nares. — (Woodcut, Pig. 15, pn ; also PI. XXVIII, fig. 3, pn.) — The 

 internal nasal aperture is a longitudinally elongated oval opening, 2 inches in 

 length, and one in breadth in the adult, and its margin is tloick and fleshy. Its 

 posterior border is sUghtly behind the posterior margin of the basi-occipital bone. 

 It dilates between its margin and the posterior end of the pterygoid into a sac which 

 fills up the downward and outwardly projecting plate of the basi-occipital and 

 basisphenoid, and runs forward to the pterygoids. The sac thus ^fills up the triangu- 

 lar surface on the base of the skuU, defined by these osseous parts, and in con- 

 sequence is of considerable capacity, triangular in form, with the apex directed for- 

 wards to the osseous nasal septum ; having a length of nearly 3 inches, and a breadth 

 of 1"50 inch. The walls of this portion of the nasal canal originate external to the 

 internal nares, so that they form a kind of imperfect floor to the sac, projecting 

 internal to its walls for nearly an inch and a half anteriorly, but only about half an 

 inch posteriorly. The front and sides of the opening are thick, wliile the posterior 



