Chap. III. The Anatomy ef a HORSE. 23 



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 directly acrols 

 one another in the form of the Letter X ; fo that their 

 A<ftion is alfo contrary: The External extending the 

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

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

 in the Breath ; whereas the Internal contra^5l the Breall, 

 by drawing the Ribs downwards towards the Breall- bone, 

 for Expiration or Expulfion of the Air. 

 Next the Mufcles, on the inlide of the Ribs, I'^^e Pleura. 

 we obferve the Pleura. It is a double Mem- 

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

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

 Nerves. It is perforated in feveral Places for the Ingrefs 

 and Regrefs of the Veflels, 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 Inter coll ah ; its Arteries from hi VeJ^di. 

 -the upper Intercojal^ and its Nerves from 

 between the Vertehrd; of the Back. 



As the Feritonaum furnifhes proper Te- , j^^ 

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

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

 contain'd in the Cheft, which it involves on all Sides. \x. 

 is likewife a Defence to the Intercojlal Veflels, which runs 

 between its Membranes, preferving them from being grea.t- 

 cd and hurt by the Ribs. 



The Diaphragma or Midriff, which di- ^he Diaphrag- 

 videe the Cheft from the lower Belly, comes ma or Midriff > 

 next in Order. It is a thin Subftance, but- 

 mufcular and flcfliy, arifmg, according to fome, from its 

 Circumference ; and according to others, from the flefhy 

 Productions, which fpring from the Vertehrcs of the 

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

 The Diredlion of its Fibres are from its Back and inner- 

 mofl: Part of nervous Body, branching out on each Side to 

 its Circumference towards the Ribs. It has feveral Per- 

 forations, or Paflages for the Nerves and large Blood- 

 4C4 veiTels^ 



