Read Ebook: Thoracic and Coracoid Arteries In Two Families of Birds Columbidae and Hirundinidae by Jenkinson Marion Anne

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INTRODUCTION 555

METHODS AND MATERIALS 556

MYOLOGY AND ANGIOLOGY: HIRUNDINIDAE 557 Myology 557 Angiology 558

MYOLOGY AND ANGIOLOGY: COLUMBIDAE 560 Myology 560 Angiology 560

SUMMARY OF ARTERIAL ARRANGEMENT 562

DISCUSSION AND CONCLUSIONS 562 Individual Variation 562 Intrafamilial Differences 563 Interfamilial Differences 565

SUMMARY 567

LITERATURE CITED 573

INTRODUCTION

Most descriptions of the circulatory system of birds, largely the work of Glenny, have dealt with arteries of the neck and thorax in a wide variety of species. As a result of his work, Glenny offered several hypotheses concerning the phylogenetic, hence taxonomic, significance of differences in some of these vessels. He also described six types of thoracic arterial arrangements and stated that these categories might represent various levels of evolution .

The families Columbidae and Hirundinidae have two nearly extreme arterial types described by Glenny, and are universally acknowledged as monophyletic. Differences within the families, therefore, can be considered as valid intrafamilial differences. I have investigated the thoracic and coracoid arteries and their branches in members of these two families to determine the degree of individual variability of the vessels, and the possible causes of interspecific and intrafamilial differences.

METHODS AND MATERIALS

All specimens studied are in The University of Kansas Museum of Natural History. They were preserved in alcohol and their blood vessels were not injected. Dissections were made with the aid of a binocular microscope at magnifications of 10x and 20x.

Family Columbidae

Family Hirundinidae

The following sources have been particularly useful for the terminology of muscles and of skeletal features: Ashley , Beddard , Coues , Howard , Howell , and Hudson and Lanzillotti .

The names used for most arteries are those in common usage for vertebrates. I have not used the terms "internal mammary" and "intercostal" artery as substitutes for "thoracic" artery, except when referring to the work of others. The vessel's homology with the internal mammary artery of mammals has been denied , and the name "mammary" is certainly not useful descriptively in birds. The term "intercostal" is less objectionable, except that such a name may call to mind segmental vessels arising from the dorsal aorta. The term "thoracic" seems best, as it is reasonably descriptive, and has been used by Glenny in the majority of his descriptions covering a wide variety of birds. The name "sternoclavicular" has been used by others as a synonym for the "coracoid" artery. I have arbitrarily chosen to use the latter.

ACKNOWLEDGMENTS

MYOLOGY AND ANGIOLOGY: HIRUNDINIDAE

Myology

Angiology

Figs. 3 and 4 show all arteries discussed for this family. The numbers following the names or descriptions of arteries in the text refer to numbered arteries in one or both of these figures.

Between the origin of the coracoid artery from the subclavian, and the point where the coracoid artery passes the medial edge of the coracoid, several branches are given off. These vessels are highly variable in origin, as described below, and not all were always found. Along with the coracoid artery, they are termed a "coracoid complex."

From the ventral trunk of the thoracic artery a variable number of small vessels arises to supply the costosternal articulations. The main ventral trunk bifurcates into two branches, one of which passes onto the inner face of the sternum, and one of which supplies the posterior two intercostal spaces.

MYOLOGY AND ANGIOLOGY: COLUMBIDAE

Myology

Angiology

Figs. 5, 6, and 7 show all arteries discussed for this family. The numbers following names or descriptions of arteries in the text refer to numbered arteries in one of these figures. Insofar as possible, the numbers used for these arteries are the same numbers used for the homologous vessels in swallows.

All vessels of the coracoid complex are exceedingly variable, in number, size, and site of origin.

SUMMARY OF ARTERIAL ARRANGEMENT

DISCUSSION AND CONCLUSIONS

In the vessels studied individual variation is marked, but the arterial arrangement within both families is relatively constant. Interfamilial differences probably represent responses of the arteries to adaptive structural differences of other systems of the body.

Individual Variation

The term "individual variation" is used here to mean "continuous non-sex-associated variation" found between members of the same species or between the two sides of the same individual. It is hazardous to define individual variation in the origin of one vessel by relating its location to other vessels, because these may likewise vary in origin. But, by necessity, certain vessels that are probably less variable have been considered here as being constant in origin. If these three vessels are accepted as reference points, individual variants, as well as interspecific differences, can easily be described in the thoracic and coracoid arteries and in their various branches.

Intrafamilial Differences

In spite of the rather extensive amount of individual variability in some vessels, I found the over-all pattern of arteries to be relatively constant within the family Columbidae and within the family Hirundinidae. There are, nevertheless, several intrafamilial differences needing some further discussion and clarification.

Bhaduri and Biswas have suggested that "the accessory sternoclavicular artery occurring sporadically as it does in some species of diverse groups may not have any phylogenetic value."

Interfamilial Differences

As shown above, there is a high degree of individual variation in the vessels being considered, while at the same time, few interspecific differences were noted within the families. On the other hand, the vascular arrangement of swallows consistently differed from that of pigeons in the species studied. The differences are most easily described by discussing the resulting change in the site of origin of the thoracic artery. In swallows the thoracic artery arises between the carotid and axillary arteries, either from the stem of the coracoid artery or independently from the subclavian, but in pigeons the thoracic artery arises from the pectoral stem, a site of attachment that is relatively more lateral than in swallows.

A comparison of these suggestions with statements made previously about these arteries seems necessary. When Glenny summarized his accumulative findings, concerning the main arteries in the region of the heart, based on individuals representing more than 750 avian species of 27 orders and 120 families, he described five types of thoracic arteries that were distinguished by differences in the site of their origin, and one type in which there were two thoracic arteries on each side. His statements regarding these differences were as follows :

"The thoracic, intercostal, or internal mammary artery of birds... is found to arise at slightly different relative positions--from a point at the base of the inferior pectoral artery to a point near the base of the coracoid or sternoclavicular artery, and in some instances both of these vessels have a common root from the subclavian artery. Such differences are found to be of common occurrence within several orders of birds. In the Galliformes and the Passeriformes there appears to be a graded series in the sites of attachment of the thoracic artery from a lateral to a medial position. As a result of these observations, numerical values can be assigned to the site of attachment of the intercostal or thoracic artery, and these values may come to be used as an index in specific levels of evolution....

"The medial migration of the thoracic artery appears to have some phylogenetic significance as yet not understood."

The six types of thoracic arteries described in Glenny's classification were distinguished as follows :

"Type 1: attachment to the pectoral stem lateral to the axillary.

"Type 2: attachment to the subclavian between the axillary and coracoid.

"Type 3: attachment to the subclavian at the base of the coracoid.

"Type 4: attachment to the subclavian, but with a common root for both the coracoid and thoracic.

"Type 5: attachment to the subclavian medial to both the axillary and coracoid.

"Type 6: two separate thoracic arteries are present; the primary thoracic is the same as type 1 above, while the secondary thoracic is the same as type 3 or type 4 above."

Possibly the thoracic artery has undergone migration but apparent differences in its origin might well be due to differences in other vessels of the thoracic area. Additionally, there seems to be no reason to assume that the lateral position of the thoracic artery is the primitive one, or that the medial is the derived position, as is implied by the phrase "medial migration." Although the lateral site of attachment is predominant in the lower orders of birds, and the medial attachment is found primarily in Passeriformes, a fact which may indicate that type 1 is the more primitive, it must nevertheless be kept in mind that a sequence of a single morphological character does not necessarily represent the phylogenetic sequence of the character itself .

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