\rr \i; r/rs i\ 



membranous folds which partition its cavity. Tin- meiiibr.me forming it In-ing continued 

 If, every organ traversing the thorax beoomea the OMM >!' ;i t'..ld in which it is 



illi]>risonr<l : ami a- tli.- tlmr-idc cavit\ i- tra \er-ed by the t:a -In-a ami the fr.sxijiliau'ils. the 

 mnsd.-s which muse tlic inferior larynx, ami the arteries ami vt-ins, it will be under-i ."1 

 how tlii.- reservoir should l>.-ci>nn i irr-irular in consequence ut' these arions jait 

 ami ;iN why tin- I'tli.-r si-rial sa -s situated between tin- VIM-ITU ami tin- walls of the 

 thorax, or the simple contiguous surfaces, should preserve their regular ami pr-'per 

 farm. 



I'hc thoracic n-ervoir communicates with the lungs by an infundibular orifice, 

 situ. tied mi tl:.- i At. rnal side of the embouchure of rarh bronchus. This orifice i- 

 ililatcil ilnrinic inspiration, by the contraction of the two tir.-t fasciculi of the pulmonary 

 diaphragm." 



'2. < serroir* (Fig. 246, 1, 1). "They are situated above tin- preceding. 



and tin- inferior part of the neck ami anterior part of the hint,'; inflated after removal 

 from tlii- neighbouring parts, they resemble two cones, whose rounded base looks 

 for wards, ami whose ] -didi ad d summit is din-cte 1 backwards. 



"Superiorly, thes.- n si rvoirs lie against the cervical muscles; inferiorly, they corn -- 

 pond to the air-sac of the thorax, from which they are separated by tin- trachea, the 

 resophagus, the pnemnogMtlia nerves, and the jnirnlar veins. Inwardly, they are in 

 juxtaposition, and consequently form a median septum which includes in its substance 

 the two . -,.111111. n carotid arteries. Outwardly, they arc related to the origin of the 

 to each of which they furnish a small sheath, and with the vertebral 

 artery which they surround, but do not contain in their cavity, as well as with u 

 siiln'.it;i!ienus inns. ! and the skin. By their summits, they c.mimnnieat'.- with the 

 anterior diaphragmatic bronchus ; and by their base they send out a prolongation which 

 conducts the air into all the vertebra; of the neck and back, intj all the veitebral ribs, 

 and. tinally. into the spinal canal. 



In their cervical iwrtion, these prolongations present themselves in the form of two 



:idingfrom the base of the cervical reservoirs to the base of the cranium, 



\\li.ie they termin-.ite ; parallel and contiguous to the vertebral arteries, like them 



lod#d in the canals excavated in the substance of the transverse proe 

 " From their external p.irt arises, at the six last cervical vertebrae, as many diverticnli, 

 which, lying against each other, pass from each side in the muscles of the neck, sur- 

 rounded by a common fibrous envelope, and apparently form a kind of canal nt the 

 inferior part of this region ; win n, however, this fibrous membrane is removed, it 

 becomes easy to isolate them, and it is then seen that they are completely independent. 

 and resemble .-mall cornua. Highly developed in Palmipeds, they are only present in u 

 rudimentary state in the other classes. 



t >n the internal side of these conduits, we see, at the level of each vertebra, one or 

 more or tio-s by wh : di the air enters their interior ; and at the int-i vi-rtebral foramina 

 another oritice. \\hidi allows it to pass into the spinal canal. From the communication 

 established by tin se or tic.-s lM:tw.en the re.-p irat- n\ apparatus and the spinal canal, it 

 follows that in birds the ct-rvieal region istiavers.-d by three atmospherical currents 

 iteral or intertt.i | arallel to the vertebral arteries; the third medi: n or 



iiial. parallel to the spinal cord. 



.lu.-t as the medullary t'.-.-ue i> replaced by air in the bones of birds, so might it ! 



M-d that the sub-aradinoide.in fluid was also rep'ared by air around their spinal 



cord : and <>\ rvittion justifies the correctness of this prevision. The dura inati-r, w !.">< 



caiwcity is so sujK-'rior to the voluine of the marrow in Mammals. -\a -tly nn usurps the 



volume of that organ in birds; sr> that there does n. rw. en the fibrous ainl 



ner\Miis surfaces any space for an nccumulation of liquid ; this an:>t->ini<-al fact ;- 



Miilicii-nt to d--iiionstiate tin- a'-s nee of .snl>-anichnoid.-i.n lluiil in Liids. In deii\ ing the 



this fluid, it ouirht to U- added that in this class of v.-i tebr.ita. as in th<- 



preceding, the .-jiinal prolongation is covered by a triple eiiv. \\H- ; that in a -h. I. t\s. . i 



tin- pia nntt-r and dura mater, is found a th n tr.msptn-nt meinbnim-. \\hii-h is lubri- 



cated by a serous fluid; but here this fluid d>cs not collect, it only nn.i~t.ns tli, 



id inenibiane. 



iisid. -red in their dorsal portion, the prolongations spiin^inu' from ti 



tier an entirely dillerent arrangem.-nt to that already n..:i. I mter- 



xi.inal current, ha\inu' ent. red tin tin. ran. terminates by passing into the first dorsal 

 vertebra; after c..iir-in<_' through <-\ery part of this veitehra, it escapes by a I) 



i the two ih>t libs, nt the ori-.'inoi the tirst ilorsal 



fr..m this .. ;l ,-, n pa s jut., the -, c,,nd vert.-bra by an ojH-niii,' jila.-id 

 hit- r.il p.irt. then it tln^s ba'-k from this into a new iiir-sa.- d. \dojH-d b, t 

 uid third rib.s; and p s-inir in the -ame manner into the thud v rt> 



