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by their combined form and articulations, the head resting on them 

 is provided with an equatorial and azimuth motion, as the astrono- 

 mers say. The pairing of the 1st and 2d ostcologically, is further 

 strengthened ngurologically, which is also applicable to the next pair 

 of the 3d and 4th. These two pairs are more properly to be consi- 

 dered as the acostal cephalic portion, as the cervical plexus is princi- 

 pally distributed to the upper region of the body, as fivr as the nioto- 

 sensory part of the system is concerned, although it also contributes 

 to the thoracic and abdominal portions of the nutrient or splanchnic 

 system. The third pair, formed by the 5th and 6th cervical ver- 

 tebne, are the acostal constituents of the humero-brachial regions, and 

 with tho 7th, 8th, 9th, and 10th, are ncurologically connected to- 

 gether in supporting the nerves, forming the brachial plexus as they 

 emerge from the spinal canal. This arrangement completes tho cervical 

 region in all the mammals except the Bradipus tridactylitis ; which is 

 also illustrative of the coupling or pair principle here proposed, as 

 the additional vertebrae only form another pair. The idea of the dif- 

 ferent classes of vertebra3 composing the cervical region, as pi-oposed 

 by De Blainville and Knox, was examined, and shewn to bo incom- 

 plete, as it considered the 7th vertebra to be a class by itself. As De 

 Blainville's view coincided with that now submitted, in separating the 

 7th from the upper vertebrae, it was pro tanto adduced in evidence ; 

 but the most striking corroboration was found in the examination of 

 tho skeletons of many of the mammals, several of which were ex- 

 hibited and demonstrated, where it was shewn that in many, if not 

 all, mammals, the normal position of the head of the rib was opposite 

 the intervertebral space, and that as 12 ribs require 12 spaces, there 

 must be 13 costal vertebra;. This additional thoracic or costal 

 vertebra is provided by the 7, which is only (in man) deprived of 

 its costal connection possibly by the traction of the subclavian artery, 

 which is tho remains of one of the primitive reptilbid branchial 

 arches, even here the first rib is occasionally in its normal situation, 

 and when it is found that, in all cases, there are in man eight and 

 generally nine of the ribs in their normal situation, and, also, that 

 an undue sharo is given to the 8th vertebra, as the whole of the 1st, 

 and part of the 2d, rib is connected to it, we are surely authorised 

 to consider this as the normal position in all mammals. The impor- 

 tance attached to this osteological discovery is, that it corrects an 



