62 DK. If. H. ALCOCK ON THE VASCULAR [Feb. 1, 



lif/amentum latum j^n^^^ionis proceeds outwards to the posterior 

 lobe of tlie left lung, very much as in man. 



The pleura of the right side extends upward from the sternum 

 until it reaches the pericardium. Anteriorly it is folded around 

 this, and reaching the root of the right lung becomes continuous 

 with the visceral layer. Posteriorly, this reflexion of pleura 

 passes upwards until it reaches the postcaA'al vein, which has an 

 intra-thoracic course of some length — 7 mm. in this species. 

 Turning round the vein the pleura retraces its course, forming 

 thus a median recess or pouch, in the posterior part of which 

 lies the azygos lobe of the right lung, the anterior part being reduced 

 to a mere chink by the near approach of the pericardium towards 

 the diaphragm \ The pleura finally leaves the anterior thoracic 

 wall in company with the pleura of the left side, considerably to 

 the left of the mesial plane. The ligamentum latum pulmonis 

 passes to the posterior lobe of the right lung from the reflexion 

 of pleura thus formed, lying dorsal to the azygos lobe. 



The Lungs. 



Following the nomenclature of Aeby '\ four lobes may be 

 distinguished in the right lung — anterior, middle, posterior, and 

 azygos : and two in the left — anterior and posterior. This agrees 

 with the description of Eobin ^, whose careful and accurate work 

 leaves little to be added by subsequent investigators. 



The right lung is considerably larger than the left, and the 

 main lobes of each are much subdivided by secondary fissures. 

 The morphology of these, as well as an account of the pulmonary 

 arterial and venous sj^stem, will be found in Part II. of this paper. 



The relation of the lungs to the ventral wall of the thorax 

 would appear to vary somewhat. Robin ^ describes the posterior 

 lobe of the left lung as extending across to meet the middle lobe 

 of the I'ight lung, lying beneath the base of the heart and great 

 vessels. In my specimens, shrunk a little by immersion in spirit, 

 this was not the case (fig. 1), and in transverse sections of Vesper lujo 

 noctula and Rhinolophus hijyj^osidei'os, with the organs carefully 

 hardened in situ, there was still a considerable interval. 



The anterior lobe of the left lung crosses the mesial plane ventral 



' I was interested in observing in a dissection of a Dromedary an inter- 

 mediate stage between the condition found in Pteroims and in man. In that 

 animal, anteriorly the pleurie of both sides pass upward in the middle line 

 from the sternum, forming a definite mesial partition. Posteriorly, the 

 arrangement is exactly similar to that described above, except that the median 

 rece^s is much reduced in size, owing to the smaller development of the azygos 

 lobe. The pleura is stroiig and tough, and can be followed out with the 

 greatest ease. In man, the azygos lobe has altogether disappeared in the adult, 

 and the pleural recess is reduced to a minimum {'mcdiastino-dlaphragmatic 

 sinus," Macalister, Human Anatomy : London, 1880, p. 316). 



- Aebv. — Der Bi-onchialbaum der Saugethiere, etc. Leipzig, 1880. 



^ EoBiK, H. A. — " Recherches etc." v. supra. See also on this subject, 

 Daubenton (Buft'on and Daubenton, Hist. Kat. x. p. 70, 17H3). Owek (Comp. 

 Anat. of Yertebr. iii. p. 577), and CuviEii (Anat. Comp. L'nd ed. vii. p. 151). 



