426 



ANATOMY OF VERTEBRATES. 



28 S 



apterus) are large, and ascend into view at the back part of the 

 nostrils, where they coalesce with the frontals. The small nasal 

 bones are wedged into an interspace between them and the frontals 

 at the summit of the nasal apertures. 



In Hyperoodon the skull is remarkable for the developement of 

 the outer border of each maxillary bone into a broad and lofty 

 vertical crest, and for the backward prolongation of the posterior 

 border of the same bones to the occipital region, where it is de- 

 veloped into what seems to be an occipital crest. In Platanista, 

 the corresponding borders of the maxillary, after rising to the 

 vertex, are reflected forward, converging, so as to overarch like a 

 domed roof the circumnarial part of the skull. In Euphysetes 

 this concave space is divided behind the nostrils by a vertical 

 ridge. Euphysetes simus ^ shows the opposite extreme to BalcBna 

 and Physeter, in the disproportionate shortness of the rostral or 

 * prenarial ' to the cranial or * postnarial ' part of the skull. In 

 ParazipMus the vomer is singularly tumid and dense. 



The hyoid arch consists, in BalcB7iid(B, of a pair of stylohyals, 

 fig. 288, 38, ligamentously connected with the mastoids, and 



similarly attached by fibrous re- 

 presentatives of ceratohyals, 39, 

 to the pair of processes at the 

 fore part of the basihyal, 4i. 

 This large, broad bone is pro- 

 duced outwardly into a pair of 

 compressed bars, thicker than the 

 stylohyals, and representing the 

 thyrohyals. 

 C. Bones of Limbs. — The clavicle is absent. The scapula is a 

 flat triangular plate, with one angle truncate to form the glenoid 

 cavity for the humerus, and without the ^ spine ' along the 

 outer surface. In Balcena, figs. 159, 289, 51, the triangle is 

 almost equilateral, with the side forming the base rather convex, 

 and the part supporting the truncate angle, by somewhat produced, 

 forming a ' neck.' The acromion, a, projects forward from the 

 outer part of the neck near the anterior border. In Balcenoptcra 

 the base is proportionally longer than the other two sides, and 

 forms a more convex border : in Bal. longimana, Kud., the 

 acromion is obsolete, and the coracoid is merely an obtuse pro- 

 duction of the fore part of the glenoid cavity. In the Cachalot 

 (^Physeter), the convex base is the shorter side of the triangle, the 

 vertical exceeding the antero-posterior diameter of the scapula : 

 the acromion is longer and larger than in BalcenidcB, and there is 



Hyoid arch, Balcenoptera. 



