Chap. IIL The Anatomy of a HORSE. 2 5 



The External take their Rife from the lower Part of 

 the upper Ribs, and end in the upper Part of the lower ; 

 and the Internal, from the upper Part of the lower Ribs, 

 ending in the lower Part of the upper : By which means 

 they not only differ in their Origins and Infertions, but 

 alfo in the Courfe of their Fibres, which run diredly acrofs 

 one another in the form of the Letter X j io that their 

 Adion is alfo contrary: The External extending the 

 Cheft, by raifing the Ribs, and drawing them backwards, 

 help to make room for the Air in Infpiration, or taking 

 in the Breath ; whereas the Internal contrav5l the Breaft, 

 by drawing the Ribs downwards towards the Breaft-bone, 

 for Expiration or Expulfion of the Air. 

 Next the Mufcles, on the inlide of the Ribs, 'The Pleura, 

 we obferve the Pleura. It is a double Mem- 

 brane, which fprings from the infide of the Spine j and is 

 believ'd by fome to take its Origin from thp Coats of the 

 Nerves. It is perforated in feveral Places for the Ingrefs 

 and Regrefs of the Vcflels, which go from the Heart to 

 the Head, and the Veins which return from thence; as alfo 

 for fuch as go downwards to the lower Belly and Extre- 

 mities, and thofe which return from thence to the Heart. 



Its Veins are from the Vena fine pari, 

 and upper Intercojlals ; its Arteries from ^(^ Vejfels. 

 the upper IntercoJlaU and its Nerves fironi 

 between the Vertebra of the Back. 



As the Peritonaum furnifhes proper Te- „ j. 

 guments for all the Vifcera in the lower ^^ ■'^' 

 Belly, fo this performs the fame Office to all the Parts 

 coniain'd in the Cheft, which it involves on all Sides. It 

 is likewife a Defence to the Intercojlal Vefl'els, which runs 

 between its Membranes, preferving them from being great-, 

 ed and hurt by the Ribs. 



The Diaphragma or Midriff, which d;- <rhe Diaphrag- 

 vides the Cheft from the lower Belly, comes ma or Uidrijf^ 

 next in Order. It is a thin Subftance, but 

 mufcular and fleftiy, arifing, according to fome, from its 

 Circumference ; and according to others, from the flefhy 

 Produftions, which fpring from the Vertehrcs of the 

 Loins. Its Middle is nervous, and its two Sides flefhy. 

 The Dircdtion of its Fibres arc from its Back and inner- 

 inoft Part of nervous Body, branching out on each Side to 

 its Circumference towards the Ribs. It has feveral Per- 

 forations, or Pafiages for the Nerves and large Blood- 

 C 4 velTels, 



