298 STRUCTURE OP THE SHEEP. 



like a piece of parchment on the inside of a rummer glass 

 The skull in quadrupeds is composed of upwards of thirty 

 bbnes, which are connected together by dove-tailed sutures. 

 It used to be considered that the object of this extensive di- 

 vision of the bones was the convenience of ossification, which 

 always commences at the centre ; but a more extended view 

 has discovered other wise purposes ; for not only is the dove- 

 tailed suture the strongest mode of union, but it is also the 

 best adapted for securing the brain from injury, as it yields 

 considerably to the impression received, and thus wards off 

 both concussion and vibration. There is an exception, how- 

 ever, to this usual connexion in the temporal bones which 

 form the sides of the cranial cavity, and which are connect- 

 ed to the other bones by what is termed the squamous suture 

 — one bone, in fact, simply overlaps another. This union is 

 inferior in strength to the former ; but nature has here another 

 oflSce to perform, and the reason of this exception will at once 

 be comprehended on examining the skull. If a considerable 

 blow be received on the upper portion of the! arch, its sides 

 are the parts most likely to give way ; and to guard against 

 this consequence, the under bone overlaps the upper, and 

 Ihus acts like the tie-beam of an arch in keeping the parts 

 together. This dove-tailed suture does not connect the bones 

 of the inner table ; for, though ar<;arpenter might find this mode 

 of union serviceable in joining the sides of a wooden box, it 

 would by no means be found applicable in connecting togeth- 

 er brittle substances, as it would be extremely liable to chip 

 off at the edges. 



The cranial cavity, or that part which contains the brain, 

 is not more than a third the size of the other parts of the 

 skull, the remaining portions being devoted to mastication 

 and smelling. 



There are no less than nine bones which enter into the 

 composition of the cranium. The two frontal bones form 

 the anterior part usually called the forehead ; but the inter- 

 nal plate of these bones separates and recedes from the ex- 

 ternal plate so as to form a cavity between them, which is 

 called the frontal sinus, and is divided by a septum or ridge 

 of bone between them. The internal plate forms a covering 

 for the anterior lobe of the cerebrum. In horned sheep the 

 separation of the plates of the frontal bones is considerably 

 greater than in others. The horns proceed on each side 

 from the frontal bone, and seem, as it were, prolongations of 



