THE HEAD. dC 



D, and give way sometimes as represented at E. la a dome the 

 weight of the materials constantly acting may he considered as 

 •p- ^ representing the force applied at 



B ; and so great is the lateral 

 pressure, or tendency to hulge 

 out {vide D and E), that it is 

 necessary either to dove-tail the 

 materials into one another, or to 

 pass strong iron chains round 

 them. For want of sufficient 

 attention to this, " the dome of 



St. Sophia in Constantinople, 



C built in the time of the emperor 



Justinian, fell three times daring its erection ; and the dome of the 

 cathedral of Florence stood imfinished an hundred and twenty 

 years, for want of an architect." 



Nature, in the construction of the horse's head, has taken 

 away the pressure, or removed the probability of injury, -by giv- 

 ing an additional layer of bone, or a mass of muscle, where 

 alone there was danger, and has dove-tailed all the materials. 

 Farther than this, in order to make assurance doubly sure, she 

 has placed this effectual girder at the base, in the overlapping 

 of the squamous portion of the temporal bone. 



Above the parietais, and separated from them by a suture 

 (fig. g. Fig. 2, and fig. e, Fig. 3), is the occipital bone. Supe- 

 riorly it covers and protects the smaller portion of the brain, the 

 cerebellum ; and as it there constitutes the summit or crest of 

 the head, and is particularly exposed to danger, and not pro- 

 tected by muscles, it is interesting to see what thickness it 

 assumes. The head of the horse does not, like that of the hu- 

 man being, ride upright on the neck, with all its weight sup- 

 ported by the spinal column ; but it hangs in a slanting position 

 from the extremity of the neck, and the neck itself projects a 

 considerable distance from the chest, and thus the whole weight 

 of the head and neck is suspended from the chest, and require 

 very great power in ord Br to support them. 

 How is this weight tc be supported ? 



From the back of the occipital bone (fig. y. Fig. 3), and im- 

 mediately below the crest, proceeds a round cord of considerable 

 bulk, and composed of a ligamentous substance, which reaches 

 down and is securely attached to the spines of the vertebrae, or 

 bones of the back ; and by this ligament — ^the ligamentum 

 colli, ligament of the neck — the head is supported. 



There are, however, some admirable contrivances connected 

 with this ligament. As it proceeds from the head, it is in the 

 form of a round cord. It passes over the atlas, or first bone of 



