50 



THE BONES. 



Differential Characters of the Parietal Bone in other Animals. 



A. Ox. — The parietal bone in the Ox does not occupy the anterior aspect of the head, but 

 concurs with the occipital to form the base of the neck. It represents a very narrow osseous 

 plate, elongated transversely, and curved at its two extremities, which descends into the 

 temporal fossae to rest upon the sphenoid bone. There are no parietal ridges. The internal 

 protuberance is only marked by a slight elevation of the internal plate ; for the most part it 

 belongs to the occipital bone. The parietal bone of the Ox is developed from three centres 

 of ossification, and the middle nucleus is even primarily divided into lateral halves ; but these 

 centres «re consolidated with each other at an early period, as well as with the anterior 

 portion of the occipital. It does not aid in the formation of the 

 parieto-teniporal canal, and is excavated internally by cavities 

 which communicate with the frontal sinuses. 



B. Sheep, Goat.— The parietal bone of the Sheep and Goat 

 is relatively much larger than that of the Ox. It participates in 

 the formation of the parieto-temporal canal, and has no sinuses. 



C. Camel.— This bone occupies the anterior face of the 

 cranium ; but it is long, narrow, and deeply lodged between the 

 squamous portion of the temporal bone and the frontal bone, to 

 rest on the sphenoid. The parietal crests, thin and elevated, lie 

 against each other for nearly their entire lengtli, and are not pro- 

 longed to the frontal bone (Fig. 45). These crests do not exist at 

 an early age. 



D. Pig. — The parietal bone is very thick ; it has two very 

 marked crests, which do not meet at their upper part (Fig. 28). 



E. Dog, Cat. — In the Dog, the parietal bone is distinguished 

 by the great development of the temporal crests (Fig. 2li). 



In the Cat there are scarcely any parietal crests, and the in- 

 ternal protuberance is replaced by two great transverse bony plates, 

 which separate the cavity of the cerebrum from that of the 

 cerebellum. 



F. Rabbit.— Almost quadrilateral, the parietal bone of the 

 Rabbit has its temporal crests carried to near its lateral borders. 



3. Frontal Bone (Fig. 26). 



The frontal is a flat quadrilateral bone, the sides of 

 which are bent in the middle at an acute angle, and are 

 carried back, and a little inwards, to meet the wings of 

 the sphenoid bone. It assists in forming the cranial roof 

 and part of the face. It is bordered : above, by the 

 parietal bone ; below, by the nasal and lachrymal bones ; 

 and on each side, by the temporal bones. It offers for 

 study an external and an internal face, and four borders. 



Faces. — The external face is divided, by the double 

 flexure of the bone, into three regions : a middle and 

 two lateral. The first, nearly plane, is lozenge-shaped, 

 is covered by the skin, and constitutes the base of the 

 forehead. It gives rise on each side, at the point where 

 it is inflected, to a long process, flattened above and 

 below, which curves backward, forming the orbital arch. 

 The superior or external face of this process is convex and slightly roughened ; 

 the internal face is smooth and concave, and forms part of the orbital fossa. Its 

 posterior border, thick and concave, is continued, inwardly, with the correspond- 

 ing parietal ridge, and outwardly with the superior border of the zygomatic 

 process. It limits, in front, the temporal fossa. The anterior border, also 

 concave, but thin, concurs in the formation of the orbital margin ; the summit, 



head of the pig 

 (anterior face). 

 1, Summit of occipital 

 tuberosity. 2, parietal 

 bone. 3, frontal bone : 

 A, Supra-orbital fora- 

 men ; a', channel de- 

 scending from it. 4, 

 zgomatic process. 5, 

 malar bone. 6, lachry- 

 mal bone : b, Lachrymal 

 canals. 7, supermax- 

 illary bone : C, Inferior 

 orifice of the super- 

 maxillo-dental canal. 

 8, nasal bone. 9, pre- 

 maxillary bone. 



