Location of cell somata and the peripheral course of axons of the geniohyoid and thyrohyoid motoneurons: a horseradish peroxidase study in the rat

The location of cell somata of the motoneurons supplying the rat geniohyoid and thyrohyoid muscles and the peripheral course of their axons were studied by intramuscular injection of horseradish peroxidase in combination with severing the innervating nerves of these muscles. Labeled geniohyoid motoneurons were found ipsilaterally in the ventrolateral subnucleus of the hypoglossal nucleus, which separates at midlevel of this nucleus from the main hypoglossal nucleus lying near the central canal and finally projects to the dorsomedial part of the ventral horn in the transition level of the brain/spinal cord. Geniohyoid motoneuron axons mostly pass through the hypoglossal nerve, whereas axons of the motoneurons in the transition level, though much fewer in number, pass through the first cervical nerve. Labeled thyrohyoid motoneurons were found ipsilaterally to form a cell column that extends from the caudal end of the main hypoglossal nucleus in the transition level of the brain/spinal cord to the dorsomedial part of the ventral horn in the caudal first cervical segment. All their axons passed through the first cervical nerve, and thus, the rostral portion of the thyrohyoid motoneuron column, which appears to be part of the hypoglossal nucleus, is not included in this nucleus but constitutes the supraspinal nucleus, which connects the hypoglossal nucleus to the ventral horn motoneuron group. The mean cell body sizes of the geniohyoid and thyrohyoid motoneurons were 28.7 +/- 4.4 and 29.3 +/- 4.6 micrometers, respectively, and their cell body size distributions were unimodal.

The association of intracranial aneurysms and arteriovenous malformation of the brain. Case report

A case of intracranial multiple aneurysms associated with an arteriovenous malformation (AVM) is described. Three aneurysms were found arising from an enlarged anterior cerebral artery feeding an AVM. In spite of the fact that two of these aneurysms received no surgical treatment, they disappeared almost completely several months after excision of the AVM. Seventy-three previously reported cases of cerebral aneurysms associated with AVM's are reviewed, and the effect of hemodynamic stresses on the development of these aneurysms is summarized.

A case of the left innominate vein passing behind the ascending aorta

The authors observed the postaortic left innominate vein, which passed behind the ascending aorta, in the body of a 69-year-old Japanese male during dissection in 1979. In this case, no rudiment of the ordinary left innominate vein could be found in front of the arteries arising from the arch of the aorta. There are few reports of this anomaly and an extensive search of the available literature revealed only ten cases, including three in Japan. Adachi classified the postaortic left innominate vein into two types, types I and II, on the basis of the positional relation between the left innominate vein and the ligamentum arteriosum. Our case was of type I, in which the left innominate vein passed ventral to the ligamentum arteriosum and ran across from left to right behind the ascending aorta to join the right innominate vein. The embryological explanation which generally is accepted for the postaortic left innominate vein lies in the transposition of a transverse connection, which becomes the left innominate vein in a later stage of development, between the left and right anterior cardinal veins from the ventral to dorsal sides of the rudiment of the ascending aorta.