442 



2446. The atlas of the large Firmer Whale (Baleenoptera Boops). 



This specimen shows that the atlas does not become anchylosed to the axis in mature and 

 large individuals of the present species of Finner Whale. The transverse processes are 

 short, simple, obtuse and imperforate : the vertebral arteries have merely pierced the neural 

 arch. 



Hunterian. 



Family Physeteridce (Cachalots or Sperm -Whales). 



Genus Physeter. 



2447. The skull of a foetal Cachalot (Physeter macrocephalus, Linn.). 



The condition of the bones in this rare and instructive specimen permits the following 

 observations being made on the cranial organization of the present genus of Cetaceous animal. 



The bony elements of the occipital neural arch are still unanchylosed. The lateral mar- 

 gins of the anterior half of the basioccipital are produced and bent obliquely downwards. 

 The exoccipitals are much produced and expanded laterally : they are deeply notched below. 

 The superoccipital contributes the upper ends of both condyles ; it is in the form of a ver- 

 tical plate, convex from side to side ; a strong internal vertical crest is produced forwards : 

 the superoccipital is overlapped at its lower and lateral angles by the exoccipitals, anterior to 

 which it attains to the alispheuoids, and is notched externally for the reception of the upper 

 angle of the squamosals. There are no distinct parietals nor mastoids : the parietal might 

 be a thin plate partly detached and partly anchylosed to the upper broad margin of the super- 

 occipital : the lower angles of this plate, incompletely separated by a fissure, may represent 

 either the lower angles of the parietals or the mastoids ; these chiefly support the squa- 

 mosals. The basisphenoid, a thick hexagonal bone, concave from side to side below, nearly 

 flat above, is anchylosed to the alisphenoids : it is perforated or grooved by the entocarotids, 

 but has no clinoid processes nor sella turcica. The alisphenoids, perforated near the middle 

 of their base by the foramina ovalia and rotunda, have a thick quadrate plate on their inner 

 side, forming their cranial surface : they extend into a point anteriorly, and articulate with 

 both the frontal and with the parietal angle of the superoccipital. The squamosals enter a 

 groove of the superoccipital posteriorly, and receive the alisphenoid in a groove anteriorly. 

 The presphenoid and the anchylosed orbitosphenoids form the anterior wall of the cranial 

 cavity, and are perforated by the optic foramina : they articulate anteriorly with the frontals, 

 sending up a small process into the interspace at the beginning of the frontal suture, which 

 process is impressed by a blind fossa like a small foramen olfactorium on each of its sides : 

 the presphenoid unites with the basisphenoid : the posterior and lateral parts of the orbito- 

 sphenoids unite with the great alee : the whole of the under and anterior part is overlapped 

 by the vomer. There is no cribriform plate. The frontal bones are large triangular plates, 

 concave externally, with the outer and fore angle produced into a long superorbital process, 

 the channel on the under part of which contracts as it approaches the cranium into a long, 



