1909.] OF SNAKES OF THE GENUS BOA. 923 



between all of them and the Madagascar species. It is interesting- 

 to note that while the corresponding species of Corallus also 

 diflFer in the structure of the lungs, the difference is of precisely 

 the reverse kind to that which we find in Boa. For in Coralhcs 

 it is the Madagascar species * which possesses the long intra- 

 puhnonary bronchus and the Neotropical forms which have a 

 short intiapulmonary bronchus. 



§ Ao7-ta and Intercostal Arteries. 



The great variations which the system of intercostal arteries 

 shows among Serpents as contrasted with the Lacertilia is a 

 remarkable fact in the anatomy of the former order of Reptiles, 

 and is one of the many anatomical facts which prove their 

 comparative remoteness in affinity from the Lizards. Moreover, 

 the condition of these arteries appears to be quite constant 

 for a species, and even for groups of species, though the current 

 generic divisions among the Boidee are not in entire harmony 

 with the arrangement of the intercostal arteries. In a series of 

 papers f dealing with these and other points in the anatomy of 

 the Boidaj, I have got together a considerable number of facts 

 relative to the distribution of the intercostal arteries in those 

 serpents. 



I have in the present paper some new facts to add to those 

 already collected, which 1 shall describe before considering the 

 classificatory results which appear to follow from a comparison of 

 the actual facts with those already known. In Boa occidentalis the 

 aorta in the region of the liver is by no means nearly in contact 

 with the dorsal parietes. It lies at some distance within the 

 body from tlie dorsal middle line of the body. It is possible that 

 this fact of position has something to do with the differing 

 arrangement of the intercostal ai'teries shown in this region of 

 the body as compared with the posterior region of the body of 

 the serpent. In any case, in the hepatic region the intercostal 

 arteries arise singly and at considerable intervals from the ventral 

 siu-face of the aorta. There are altogether very few of them. 

 They become connected at a short distance from the dorsal middle 

 line with smaller trunks running fore and aft in close relation to 

 the middle line of the body. From these secondary longitudinal 

 arteries arise in regular pairs the actual intercostal twigs. In the 

 abdominal region of the body, as it msij be termed, near to the 

 kidneys, the intercostal arteries are different in their arrangement. 



* P. Z. S. 1908, p. 151. 



t " Contributions to our Knowledge of the Circulatory System of the Ophidia," 

 P. Z. S. 1904, vol. i. p. 331. "Notes upon the Anatomy of certain Snakes of the 

 Family Boidae," P. Z. S. 1904, vol. ii. p. 107. " Contributions to the Knowledge of 

 the Vascular and Respiratory Systems in the Ophidia and to the Anatomy of the 

 Genera Boa and Corallvs ,'' 'P . Z. S. 1906, p. 499. "A Comparison of the Neo- 

 tropical Species of Coralltis, C. cooMi, with C. madagascariensis, and on some 

 points in the Anatomy of Coralltis caninits," P. Z. S. 1908, p. 135. 



